2.1 Mission Overview and SPP Objectives

Consistent with the objectives of the Small Payloads Program, this proposal is of direct relevance to the "Magog Manifesto" of October 1994. As it will be addressing the topic of trends in the odd-nitrogen budget of the stratosphere over the past 20 years, the proposal falls clearly within the category of Understanding Atmospheric Change, identified as one of the two core areas needing future research. Specifically, the MANTRA project falls into the Priority A Program, defined as "the highest priority core program" in the area of Understanding Atmospheric Change, because it deals with the measurement and modelling of middle atmosphere species related to ozone chemistry.

Under the sub-topic of Middle Atmosphere Species and Ozone Chemistry, the "Magog Manifesto" describes some of the outstanding problems in this field, Canadian capabilities, and required measurements. The MANTRA project will touch upon or explicitly address many of the problems raised: heterogeneous chemistry, concentrations of nitrogen, chlorine, and HO_x species in the 20-km region (which is particularly difficult to monitor but critical to interpreting the role of chemical and dynamic processes on ozone concentrations), investigation of the conditions that could lead to the formation of an Arctic ozone hole, and the impact of the previous 20 years of commercial air traffic on atmospheric composition. The planned balloon campaigns will make a significant contribution to the measurement of key stratospheric species. Of those species particularly identified in the "Magog Manifesto", the MANTRA instruments will be capable of measuring all but two (ClO, OH), i.e., they will detect ozone, NO₂, HNO₃, NO, ClONO₂, HCl, and aerosols, and set limits on OClO and BrO.

The proposed mission will also take advantage of and extend Canada's current strengths in the area of middle atmosphere science, while also making an important contribution to a topic of interest to the international research community. Indeed, because the MANTRA project will take advantage of balloon measurements made in Canada 20 years ago, it provides a unique opportunity for the Canadian atmospheric science community. It will build upon the previous ballooning experience of several members of the Science Team, and help to re-establish this important method for probing the atmosphere in collaboration with an industrial partner (Scientific Instrumentation Limited). It will use both balloon-borne and ground-based versions of the AES SunPhotometer, which has previously flown on the US Space Shuttle, and on the NASA ER-2 aircraft as part of the SPADE, ASHOE/MAESA, and STRAT campaigns.

This project will bring together scientists involved in all three of the major atmospheric satellite programs supported by CSA (WINDII, MOPITT, and Odin), thereby creating a Science Team having a wealth of expertise in atmospheric remote sounding. It will also take advantage of the strong chemical transport and radiative transfer modelling capabilities at York University, recognizing the crucial role of such models in the interpretation of measurements of composition. Using leading edge work in data assimilation, it will be possible to extend the "region of influence" of both past and planned balloon and ground-based measurements and to enhance the intercomparison of these measurements. Finally, the proposed study will involve collaboration with an international partner (F.J. Murcray, University of Denver), thereby significantly enhancing the measurement capabilities by adding a high-resolution interferometer to the balloon payload.

In addition to being consistent with the guidelines of the "Magog Manifesto", the MANTRA proposal meets nearly all of the objectives of the Small Payloads Program, as detailed in the Background Document for the Small Payloads Program (Version 01, July 10, 1996). It utilizes low cost access to space, provides training to students in hardware and software development, supports Canada's industrial capability in the area of balloon launching, involves co-operation between a number of institutions, may lead to the future development of related satellite instruments, provides opportunities to communicate with the public about a highly topical issue, and finally, increases interaction with the international community.

Thus, to summarize, the MANTRA proposal falls squarely within the mandate of the Space Science Program of the CSA, as required in the Announcement of Opportunity for the Small Payloads Program. It involves the development of instruments by Canadian scientists, the launching of these instruments on a balloon platform, a measurement strategy that will result in significant new data which can be used to address the issue of atmospheric change, partnership with industry, and international collaboration.

2.2 Science Requirements

The top-level science requirements are the measurements, along with their precision and accuracy, that will be needed in order for the data to be scientifically useful. The species to be measured are NO₂ with the AES NO₂ spectrophotometer; HNO₃ with the AES HNO₃ radiometer; ozone, NO₂, O₂, and aerosol (with upper limits on OClO and BrO) with the AES photodiode array spectrometer; ozone and NO₂ (again with upper limits on OClO and BrO) with the AOTF spectrometer; and HNO₃, NO, ClONO₂, HCl, and CFC-12 with the high-resolution interferometer. The ground-based zenith-sky grating instrument, photodiode array spectrometer, Brewer spectrophotometer, and ozonesondes will provide supporting measurements of total columns and profiles of both ozone and NO₂.

The final data products from the campaign will be vertical profiles of ozone, NO₂, HNO₃, NO, ClONO₂, HCl, CFC-12 and aerosol, obtained from an intercomparison of the results from the different measurement techniques. If the AES high-resolution scattering spectrometer is also flown, then profiles of OH will be measured as well. Upper limits for OClO and BrO will be established. The overall accuracy of the measurements will be improved by having a suite of complementary instruments. Table 3 presents a list of the primary species to be measured, their expected concentrations and the accuracies that should be achieved during the MANTRA mission. The vertical resolution of the profiles will be about 5 km, and possibly as good as 1 to 2 km with limb-scanning observations.

If vertical profiles of the specified constituents are measured to these expected accuracies, then it will be possible to compare these data with the historical Stratoprobe measurements and interpret them using photochemical models and possibly data assimilation. The MANTRA project will then have successfully achieved its primary scientific objectives, as specified in Section 1.1.3.

Table 3. The species to be measured during the balloon mission, along with their expected range of concentrations and expected accuracies, assuming a vertical resolution of 5 km. OD refers to optical depth units in the tangent path, for solar occultation and a 5-km layer.

2.3 Instrument Description

2.3.1 AES NO₂ Spectrophotometer

The AES NO₂ spectrophotometer is an antecedent of the Brewer Ozone Spectrophotometer now used to measure ozone in more than 30 countries. It is a small, modified Ebert-Fastie spectrograph with focal length of 16 cm, equipped with a photon-counting detector system. The instrument is properly called a polychromator because it produces a high quality spectral image across a usefully large focal plane. A mechanical chopper system is used to multiplex the single photomultiplier detector between five well-defined wavebands in the 430 to 450 nm region of the spectrum. The five wavelengths (exit slits) measured are carefully chosen to lie at high and low absorption points in the NO₂ spectrum and at stationary points in the solar spectrum.

This provides a large differential absorption cross-section and a reduced sensitivity to small shifts in the precise position of the band centre wavelengths. Wavelength stability is a serious issue because of the deep Fraunhofer absorption features in the solar spectrum. These can cause large intensity changes for small wavelength displacements in the regions where their absorption changes rapidly. The high signal-to-noise ratio of the system permits its use to measure the direct solar beam (Bloxam et al., 1975; McElroy, 1976; Kerr and McElroy, 1976) over a large range of atmospheric optical depths and also to make measurements on the light scattered by air molecules from the Earth's limb (McElroy, 1985, 1988; Roscoe et al., 1985, 1990). Further technical specifications for this instrument and the following two AES instruments are provided in Table 4 below.

2.3.2 AES HNO₃ Radiometer

The AES HNO₃ radiometer is based on the balloon emission radiometer of Pick (1969). It uses a liquid-nitrogen-cooled detector and optics to make measurements of the atmospheric thermal emission in the 11.3 micron region. The emission of HNO₃ is isolated by using several different filters to provide signals on- and off-band. The instrument is pointed at about 19 elevation angle on the payload to increase the atmospheric slant path, and measurements of the atmospheric radiance profile are made during ascent or descent. The radiance profiles are differentiated with respect to height to assign a radiance change to each layer, from which the concentration of HNO₃ is calculated (Evans et al., 1976).

Table 4. Technical specifications for the three balloon-borne AES instruments: the NO₂ spectrophotomer, the HNO₃ radiometer, and the photodiode array spectrometer.

2.3.3 AES Photodiode Array Spectrometer

The AES photodiode array spectrometer is based on the AES SunPhotoSpectrometer which flew on STS-52 with Canadian Astronaut Steve MacLean and aboard the NASA ER-2 as part of the NASA Upper Atmospheric Research and High Speed Research Programs. On the ER-2 the instrument is called the Composition and Photodissociative Flux Measurement (CPFM) Experiment and is used as an absolute spectroradiometer and to provide ozone data using the technique of differential absorption spectrophotometry. The instrument has flown at 70,000 feet nearly 100 times with this program.

This instrument is based on an EG&G randomly addressable photodiode array detector, situated at the focus of an f/2 holographic diffraction grating. Spectra are recorded from spectra 300 to 785 nm at 0.5 nm steps, with a spectral resolution varying from 1.2 to 4 nm across this wavelength range. The field-of view is 2 with a sun diffuser, and 1.2 6 without it. The dynamic range is greater than 10⁶, and the signal-to-noise ratio is higher (1000:1) than that of the AES NO₂ spectrophotometer by virtue of the much larger number of wavebands measured (1024 as compared to 5). In addition, the detection of NO₂ in the limb-scan data should be unambiguous because of the large number of wavelengths and the proper handling of the Ring effect, the filling in of solar Fraunhofer lines in scattered sunlight due to rotational Raman scattering by air molecules. The comparison of the limb-scan data from the two instruments will be a valuable secondary science objective and may help to firmly establish the source of some observational problems in using the AES NO₂ spectrophotometer to make ground-based twilight sky observations (Hofmann et al., 1995).

Data will be collected by this instrument in both solar occultation mode and limb-scan mode, and will be analyzed using a spectral fitting code to determine concentration-height profiles of ozone, NO₂, O₂, and aerosol. Upper limits for the amount of OClO and BrO will also be estimated. A second version of this instrument will be flown to measure J-values of important reactions such as the photolysis of ozone and the photodissociation of NO₂.

2.3.4 ISTS/York University Acousto-Optic Tunable Filter Spectrometer

York University and ISTS will provide an acousto-optic tunable filter (AOTF) spectrometer. The AOTF instrument has been built for balloon-borne operation, under the direction of Dr. B.H. Solheim, with funds provided by ISTS. It is capable of observing ozone, NO₂, OClO and BrO in the 250 to 400 nm spectral region. Preliminary zenith-sky observations made with the prototype instrument at York University have shown that it provides good measurements of ozone and NO₂ columns, using a DOAS retrieval. In addition, a radiative transfer model has been used by Mr. C. McLinden to simulate the limb-scanning spectra that the AOTF instrument would record from a balloon floating at 40 km, and slant columns of ozone and NO₂ were successfully recovered from these simulated spectra by Prof. K. Strong, again using DOAS analysis.

The instrument, which is based on a MgF₂ acousto-optic tunable filter, has a spectral range from 250 nm to 400 nm, and a spectral resolution of 0.07 nm at 250 nm, 0.1 nm at 300 nm, 0.15 nm at 350 nm and 0.21 nm at 400 nm. The detector is a photomultiplier tube, with very low dark count. The system throughput is 5.7 10^-4 cm²sr with an external field-of-view of 0.05 half angle. The AOTF instrument consists of two cylinders mounted one on top of the other. The main cylinder is 1.5 metres long and contains the baffle, telescope optics, a filter wheel, a mercury calibration lamp, the AOTF itself and the detector (with its high voltage supply). All components except the baffle and telescope are in a sealed housing to maintain ground-level pressure. The second cylinder, 1 metre long, is also air-tight and contains the control and AOTF RF electronics which are connected to the instrument housing by three low-voltage cables. The total mass, excluding batteries, is 45 kg.

There are two basic modes of operation, solar occultation and DOAS. Both modes require balloon pointing (azimuth control) and altitude scanning (tilting platform). Solar occultation is the primary mode for most instruments and has been used on many previous balloon flights. Azimuth control of the gondola, acquiring sun pointing and tracking of the sunrise or sunset are all mature technologies and are readily available through Scientific Instrumentation Limited of Saskatoon. The DOAS observation requirements are simpler than occultation. The gondola needs to be pointed so that the AOTF instrument looks at 90 (scattering angle) to the sun during the daytime. The instrument is then scanned in altitude by tilting the platform to pre-defined angles. The AOTF instrument requires in-flight wavelength calibration which is performed, either as part of a measurement sequence or on command from the ground, using the internal mercury calibration lamp.

2.3.5 University of Denver High-Resolution Interferometer

The high resolution interferometer is a Fourier transform instrument, originally manufactured by BOMEM (Quebec City, Quebec). The instrument is owned and operated by a group led by Dr. F.J. Murcray's research group at the University of Denver, Denver, Colorado. This group has extensive experience in spectroscopic measurements and in balloon instrumentation stretching back over several decades.

The operating scenario for the spectrometer involves the use of a solar tracking system to aim the instrument at the sun and keep it there as the sun sets (or less often, rises). Very close to sunset the atmospheric path increases rapidly with time, or equivalently with solar zenith angle. This increases the path through the atmosphere by as much as 70 times the vertical air mass above the lowest point on the path. This path increase, combined with the strong weighting of absorber amount to the lowest point on the path (often called the tangent point), gives the experimenter the opportunity to retrieve concentration profiles at altitudes below the balloon, as well as some ability to determine column amounts above the balloon.

The Fourier transform instrument will be equipped with a 50-cm path-difference scanning interferometer. The optical path difference results in a high spectral resolution of 0.02 cm^-1 with medium apodization. Each interferogram takes 40 seconds to acquire. The interferograms from the two detectors will be digitally filtered, and transmitted by telemetry as well as being recorded on board. The system has two infrared detectors, each covers approximately 500 cm^-1. The first detector would cover HCl and ozone around 2900 cm^-1. The other would cover 1400 to 2000 cm^-1 to measure NO, NO₂, and HNO₃.

The instrument uses light from the central 70% of the solar disk. A servo-controlled solar tracking system keeps the sun on the entrance aperture. The primary data are obtained as the sun rises or sets, providing a rapidly changing geometric path through the atmosphere as discussed above. Each spectrum is analyzed for the total quantities of the gases in the path, the geometry is used to deduce the altitude distribution consistent with the individual spectra. The total quantity of each gas is determined by a spectral least squares matching algorithm that adjusts the amount of absorbing gas to match the spectral lines observed.

Data for some molecules can be obtained during balloon ascent if the gondola orientation is stable enough. In this process, the quantity of gas in a layer is determined by differencing the total quantity derived from a spectrum at the bottom of the layer and a spectrum at the top. This can only be done for the stronger absorbing molecules, including HCl, O₃, and HNO₃. This measurement will be attempted since it is essentially "free", but it is not clear whether the gondola stability will be good enough for the retrieval. Loss of these data will not impact the achievement of the science objectives.

The interferometer with the solar tracker and data systems weighs about 100 kg. Power consumption is 4 A at 30 V (1.5 A standby). The instrument and tracker are about 48 inches long, 20 inches wide, and 48 inches tall (at the solar tracker, about 16 inches tall on the back 30 inches). The TM encoder is about 14 by 14 by 26 inches. There are two power commands, one for the laser and heaters (1.5 A) and the other for the solar tracker, TM, and the rest of the interferometer (2.5 A). The battery pack for 10 hours full-power duration would weigh about 20 kg. An interface unit weighing about 10 kg might also be required. The downlink is 480 kbits NRZ synchronous, using a dedicated transmitter.

2.3.6 The Ground-Based Instruments

Three ground-based instruments will be operated at the launch site, in conjunction with the balloon flights. Each of these instruments will be built using additional (non-CSA) funding: the Brewer spectrophotometer and photodiode array spectrometer will be provided by AES, and the University of Toronto zenith-sky grating spectrometer has been funded by NSERC. The primary role of these instruments will be to provide vertical column abundances of ozone and NO₂ in order to constrain and verify the vertically resolved measurements that will be made by the balloon-borne instruments. In addition, they will be compared against each other, used to set detection limits for the slant columns of OClO and BrO, and used to investigate the accuracy of a relatively new technique for retrieving vertical profiles from NO₂ and ozone slant columns. In addition to these instruments, it is intended that ozonesondes also be launched from Vanscoy (funded by AES), again in conjunction with the balloon launch. These will be used to validate the ozone profiles that are obtained by the balloon-borne instruments. A more detailed description of the supporting ground-based component of the project is provided in Section 1.5.

2.4 Payload Description

The MANTRA payload will consist of the NO₂ spectrophotometer, the HNO₃ radiometer, two photodiode array spectrometers, the AOTF spectrometer, and the high-resolution interferometer. All instruments except the interferometer are to be mounted on a tilting platform to allow altitude scans and solar occultation observations. The gondola frame will carry two primary structures, each of roughly the same volume, one half housing the tilting platform and the other half housing the high-resolution interferometer. The command and telemetry package, batteries, ballast, crush pads and floatation, flight train, parachute and recovery package are all standard components which have been flown before on previous balloon flights.

The entire gondola will be swung around by an azimuth pointing joint so that the elevation pointing table can be pointed at the sun for the solar occultation observations. Prior to sunset the instruments will be pointed at roughly 90 to the sun and the tilting table scanned in altitude for the DOAS observations. On-board magnetometers will be used to provide pointing away from the sun to an accuracy of about 5 . This is less expensive than adding a second sun sensor for off-sun viewing and provides sufficiently accurate pointing for the DOAS scans.

The pointing systems for both the azimuth pointing and the tilting table are relatively old and need to be refurbished for the proposed flight. SIL will replace or upgrade sun sensors for the azimuth control and will modify the feedback system for the pointing table to allow both sun tracking mode and free altitude scan mode. A line item is provided in the budget for this work. This upgrade will benefit future balloon flights since the refurbished pointing systems can be used again on other gondola configurations. In particular, this work will not need to be repeated for any reflights of the current payload.

The payload mass budget is given in Table 5 below. The NO₂ spectrophotometer, HNO₃ radiometer, two photodiode spectrometers, and AOTF spectrometer, which will all ride on the pointing table, add to a total mass of 96 kg. The tilting table can carry 150 kg, so there is a good safety margin. The total mass of all instruments and their supporting electronics and cryogens is 217 kg. It is estimated that 30 kg of batteries will be required for a 10-12 hour flight. The total science payload is then 247 kg which is within the target of 300 kg total science payload. It should be noted that all of these instruments have already been constructed, therefore these masses are well known, and so the total mass should be quite accurate.

The individual experiments will use unregulated 28-V power provided by lithium battery packs. In some cases DC-DC supplies may be available from the gondola contractor. The estimated power requirements for the instruments are provided in Table 6. The contractor will also provide the digital telemetry system and data recording facilities. The data collected will be returned in real time and also in permanent media form after the flight has taken place.

Table 5. Mass (revised from original proposal) and volume specifications for the scientific instruments on the balloon payload.

Table 6. Revised power specifications for the scientific instruments on the balloon payload.

2.5 Facilities Description

The launch facilities will be provided by Environment Canada, which has a fully equipped balloon launching station at Vanscoy, Saskatchewan, 25 km from Saskatoon, at 52 N, 107 W. Scientific Instrumentation Limited (SIL) operates this permanent balloon launch facility. SIL and staff have been launching balloons since 1986 and building payload systems since 1974. To date, over 120 balloons have been flown by SIL. The launch area consists of paved runways (30m 760m) and two buildings for payload preparation, ground support and storage. Launch equipment includes a launch truck, two helium trailers, a spool trailer, a flood light trailer, recovery trailer and flight train equipment. Ground support includes S-Band receivers, data recorders and uplink commanding.

The maximum balloon size that can be launched from Vanscoy with the existing equipment is 22 million cubic foot (mcf) with a 500-kg science payload. We propose to launch a 16-mcf balloon with a 300 kg science payload. This is well within SIL's launch capability. The launch will be planned for turnaround in late August or early September 1998.

The gondola will be based on existing structures which have flown successfully, and will include a tilting table and sun-pointing azimuth control. The gondola can be pointed in azimuth (coarse sensor 0.5 , fine sensor 0.05 ). Sunrise acquisition is less than three minutes (one solar disc above horizon). The tilting elevation table can be pointed to 0.05 . This allows instruments to track a sunrise or sunset or to be scanned in altitude. The current drive electronics for tilting the table are part of a feedback loop which is designed to track motion of the solar disk. Modifications would be required to allow "free" altitude scans for the DOAS experiments, however, this is not a serious problem and would be included in the gondola design work.

A GPS is used to provide position and altitude information for the balloon payload. Normally a balloon swings a few degrees like a pendulum. This motion is compensated for when instruments are tracking the sun during sunrise or sunset, however, for other altitude scans the attitude or pointing direction of the instruments must be known in order to perform the DOAS recovery. It is proposed to develop a differential GPS system which will give the required payload attitude.

The science telemetry is flexible. The standard S-Band transmitter can provide PCM data at rates up to 460.8 Kbps (bits per second). We can use multiple transmitters to increase bandwidth. It is also possible to provide higher data rates if an instrument modulates the transmitter directly or if we use higher frequency transmitters. This last option requires a new ground station receiver. The data rates for the proposed instruments are all less than 460.8 Kbps and we expect to be able to use the standard telemetry system.

There is both an up and down 1200 baud serial command link. This enables commands to be sent in real time to the payload or a specific instrument and responses from the instrument to be received at the ground station. Thus one can command and confirm that the command was received in real time. This facility will be used to change instrument operation modes and to initiate in-flight calibrations. There are also various analog, VCO and pulse counting interfaces available in addition to the PCM and serial command interfaces. Data is recorded at the ground station and requires a line-of-sight view of the balloon.

2.6 Calibration

2.6.1 Calibration: AES NO₂ Spectrophotometer

The occultation and limb-scanning measurement techniques used with the AES NO₂ spectrophotometer are essentially self-calibrating. The relative change in the spectrum due to atmospheric absorbers is determined relative to reference spectra collected during the same flight. However, as part of the instrument characterization, instrument spectral bandpasses will be determined in the laboratory. The wavelength calibration is also a critical issue. In the case of the NO₂ spectrophotometer, the wavelength calibration is done using spectral emission line sources in the laboratory. The instrument wavelength stability is sufficiently good that this calibration can be applied to the stratospheric data. The wavelengths are offset to account for changes in the speed of light, and the attendant wavelength shift, that occurs when the balloon ascends and the air pressure drops within the spectrograph housing.

2.6.2 Calibration: AES HNO₃ Radiometer

The AES HNO₃ radiometer will be calibrated as a function of pressure and temperature using the radiation reference blackbody used for the flights made in the 1970s and 1980s. This will be done on-site at the Vanscoy facility before and after the flight. In order to verify the original calibration methodology, an additional calibration exercise will be carried out wherein the traditional calibration will be compared to results from the new University of Toronto MOPITT calibration facility. The calibration activities will include radiometric calibrations made on all of the gain ranges that will be used operationally and over the range of ambient pressures and temperatures that will be experienced during a balloon flight.

The blackbody reference is a massive, blackened metal plate equipped with liquid nitrogen cooling, a servo-controlled precision heating system and a collection of thermistors which are used to monitor the blackbody surface temperature. The whole system, including the data acquisition from the instrument is automatically controlled by a microcomputer-based controller. The blackbody is cooled by liquid nitrogen and heated to a specified temperature, allowing it to be operated over the range of radiances expected in the atmosphere. The temperature is determined by a set of calibrated thermistors located at various points on the blackbody surface. Calibrations are done before and after each flight and the instrument stability is tracked over a longer period.

2.6.3 Calibration: AES Photodiode Array Spectrometer

The wavelength calibration of the AES photodiode array spectrometers will be performed in the same way as is done for the NO₂ spectrophotometer, with a dispersion equation being developed to assign the correct wavelength to each pixel of the detector. The passbands of the individual elements of the diode array will be determined using the grating tilting mechanism which is part of the spectrometer. It may also be possible to use a tunable laser source to confirm the results of the internal measurements. The passbands of the detector elements will be used as weightings to calculate the effective absorption coefficient spectrum to be used for the various constituents to be fitted in the observations. Measurements of gas samples will also be done, not to determine precise absorption coefficients but to confirm that the proper values of all critical parameters have been determined (as in Brewer et al., 1973). The wavelength calibration will be validated in the flight spectra by examining the positions of solar Fraunhofer absorption features.

2.6.4 Calibration: ISTS/York University Acousto-Optic Tunable Filter Spectrometer

The AOTF spectrometer employs a simple photomultiplier tube (PMT) as its detector. PMT detectors are very stable, have very good linear response and low dark current. Pre-flight calibration of the instrument will include responsivity as a function of wavelength, linearity over the full dynamic range and dark current measurements. These will be completed using the flight optics and with each filter. Various filters may be used to reduce bright background light or to isolate a wavelength region while observing a particular species. The minimum filter bandpass is 5 nm. Each filter will be fully characterized before flight. The optical system uses a simple reflecting telescope, filters, the AOTF device and the PMT detector. All these elements are not expected to change or change very slowly so that pre-flight calibration will provide accurate characterization of the system.

The acousto-optic tunable filter exhibits a variable bandpass during a wavelength scan, however, this effect can be well characterized and is observed to be repeatable with each frequency scan. An acoustic transducer bonded to the MgF₂ crystal is driven by a radio frequency source, in the range 90 to 160 MHz. This sends acoustic waves through the crystal which interfere with light passing through the crystal, thus defining the wavelength that is transmitted. The wavelength selected depends directly on the RF drive frequency. The frequency to wavelength relation has been fully characterized in the laboratory and will be checked using the on-board mercury calibration lamp during flight.

The wavelength transmitted by an AOTF device also depends on the temperature of the crystal. The housing containing the AOTF is temperature controlled to 0.1 C which provides a measured wavelength stability of 0.0005 nm. The RF drive frequency-to-wavelength relationship and the temperature dependence will be fully calibrated on the ground before flight. During flight, the on-board mercury lamp will be used to calibrate the wavelength at predefined intervals or on uplink command. DOAS retrievals require very good wavelength knowledge, however, the observed spectra contain many well known lines which can be used to improve the wavelength registration between spectra. The pre-flight calibrations will be carried out at York University and ISTS.

2.6.5 Calibration: University of Denver High-Resolution Interferometer

The calibration of a solar occultation interferometer is relatively straightforward. The solar signal is relatively strong and the time of the measurement short, so the instrument is, to first order, invariant during the measurement. The spectrum is determined essentially by the wavelength calibration, the zero line and the 100% line. The zero line is obtained by blanking the input signal, which in practice involves either using a beam obscurer or moving the instrument off of the solar disk. The 100% line is obtained by using the fact that the instrument sees relatively small amounts of atmosphere for high sun angles shortly before the measurement. By using known regions of low absorption between the lines, the 100% point can then be obtained. The wavelength calibration is fixed by the instrument itself and is self-calibrating by identifying lines of well-known species.

There are a number of second order effects which are important in the exact retrieval of the scientific information. These are handled at a number of levels depending upon their nature, but the long experience of instrument teams with the Fourier transform technique make these relatively routine corrections.

2.7 Launch Requirements

The launch requirements are simple and are driven by the science goals. Two primary operational modes are defined, DOAS and solar occultation. The DOAS measurements will be taken from approximately noon until late afternoon. Just before sunset, the payload will be positioned to point at and track the sun during sunset for the occultation observations. This requires a float time of 10 to 12 hours, which can only be achieved at turnaround in late August or early September (without additional down-range tracking). One of the key scientific goals of the proposed mission is to compare historical data with the new measurements to look for trends. Many of the historical flights were carried out at the fall turnaround, thus the new data should be obtained at the same time in order to mitigate seasonal effects in the trending. The launch should be made between 9:00 a.m. and noon at turnaround in August/September 1998. A launch in 1997 would be too early to prepare a payload.

2.8 Operations Requirements

The launch and ground support facilities operated by SIL at Vanscoy meet all the operational requirements for the proposed launch. The University of Denver high-resolution interferometer will provide its own telemetry package. All the other instruments will be fully supported by the existing telemetry and ground support. Payload integration and calibration facilities exist at SIL, the University of Toronto, AES, and ISTS. These facilities will be used to calibrate individual instruments and to assemble the final payload. There are no special operational tasks which require new facilities.

2.9 Schedule and Milestones

The revised project schedule is outlined in Table 7 below, based on a contract start date of August 1, 1997. It is consistent with the guidelines for a balloon launch by Scientific Instrumentation Limited, as provided in Appendix A of the Implementation Plan for the Small Payloads Program (Version 01, July 10, 1996). According to Section 12.2.3 of that document, all phases (A through E) will be combined into one contract for balloon missions, and so this has been assumed for the following schedule. The schedule for the primary 18-month contract is based upon a first balloon launch on August 1, 1998. In practice, the actual date of the launch will depend on the weather conditions, and will be chosen to be as close as possible to turnaround. As turnaround may occur in late August or early September, planning for a launch as early as August 1 will ensure that the flight systems and payload will be ready well in advance.

Table 7. Revised schedule and milestones for the MANTRA project.

Preparations for flight will begin as soon as a contract is awarded by the CSA. A Requirements Review will be held at the start of the contract, tentatively on August 1, 1997, 12 months before the nominal launch date. This meeting will bring together the project team (the Principal Investigator, Co-Investigators, the CSA Project Manager, the industrial partner, students, and relevant management and technical personnel). At this time, the mission definition, design concept, and performance requirements will be established. Trade-offs between the scientific objectives, availability of standard subsystems, costs, and scheduling will be made.

All of the proposed instruments are already designed and built, or are under construction, so that further instrument design and manufacture is unlikely. Instrument integration, test, and verification will be undertaken at the University of Toronto, York University, and AES. Payload and bus design will be performed in conjunction with SIL (Scientific Instrumentation Limited).

Ten months before the launch (October 1, 1997), the Preliminary Design Review will be convened to finalize all requirements and review the preliminary design of the payload. A payload weight estimate will be specified to within 30%, the flight profile estimate will be determined, and preliminary science support requirements will be addressed.

Six months before launch (February 1, 1998), the Critical Design Review will be held, at which point all flight hardware will be given final approval. The payload weight estimate will be specified to within 10%, the flight profile will be updated as needed, and the final science support requirements will be established. The flight support system design, including thermal, mechanical, and electrical components, will be finalized. A Class II Notam will be filed, and any necessary long lead items will be ordered.

A Flight Readiness Review will be held six weeks prior to launch (June 15, 1998). At this time, the flight profile will be finalized, the flight systems hardware will have been built and tested, and the ground-station set up. Two weeks before the nominal launch date (July 15, 1998), the instruments will be shipped to the launch site at Vanscoy and payload integration will begin. Launch will take place as close as possible to August 1, 1998, as determined by the prevailing wind conditions at the launch site.

Once the launch and recovery have been completed, the instruments will be returned to their respective institutions. One month after launch, post-flight data and reports will be submitted. The First Data Workshop will be organized for six months after launch (February 1, 1999), which corresponds to the end of the 18-month contract. Preliminary data and results will be presented by the members of the Science Team. More detailed results of the data analysis and scientific interpretation will be presented at a Second Data Workshop, to be held 11 months after launch (July 1, 1999). Further dissemination of the results to the wider atmospheric science community will take place at national and international scientific meetings, and through the refereed literature.

2.10 Risk Analysis

There are four major risk areas associated with this proposal: the instruments, the launch, the data recovery, and the data interpretation.

The instruments are a low-risk item. All the instruments have been flown before in various forms and are therefore proven. Some adaptation of the instrumentation is necessary to integrate all the systems together, but this poses a very minor risk to the mission success as the electronic modifications are relatively simple and can be thoroughly tested before launch. The necessary processes and procedures to be followed to permit reliable operation in the expected environment are well-known to both the industrial partners and several members of the Science Team (e.g., Drummond, McElroy, and Murcray). All instruments will be individually tested before integration and then again as part of a full-up integration test.

The launch is the most serious risk item. Launch failure is usually traceable to balloon problems or launch conditions. The first prerequisite is an experienced launch contractor such as Scientific Instrumentation Limited. By launching in the most favourable meteorological conditions available, the launch condition risk can be minimized. The choice of launch site and launch season are major factors in this mitigation process. The choices made represent the lowest risks possible.

Balloon problems normally cause a lower than required altitude or shorter than desired duration rather than a catastrophic failure. If it is determined that these problems prejudice the scientific success of the mission, then it is proposed to refly on a short turnaround with the spare balloon This will necessarily increase costs, but represents the only way in which this risk can be lowered. It should be stated that stratospheric balloons of this broad type have been flown by various groups for more than twenty-five years with great success, so that even this is a small risk.

The data will be captured in a variety of ways, both on-board and through down-link telemetry. This mitigates the risk of data loss through telemetry problems. All instrument telemetry will be verified immediately before launch and problem corrected before balloon fill and release.

The final risk is that the data will not produce the scientific returns of the science objectives. This risk is mitigated by the mission planning exercises, relying on the combined expertise of the Science Team and other experts they bring to the problem. This risk is judged to be low due to the wide variety and length of experience of the Science Team.

2.11 Management Plan

Each of the scientific instruments, their deployment, calibration, data analysis, etc., will be the responsibility of one or more members of the Science Team. Prof. K. Strong will be in charge of the University of Toronto Zenith-Sky Grating Spectrometer, and will also be involved with the AES photodiode array spectrometers. Dr. C.T. McElroy will have primary responsibility for all of the AES instruments: the NO₂ spectrophotometer, the HNO₃ radiometer, the Brewer spectrophotometer, the ozonesondes, and the radiosondes, although other co-investigators will also participate in the calibration of these instruments and the subsequent data analysis and interpretation. Dr. B.H. Solheim will have sole responsibility for the ISTS/York University AOTF spectrometer. While Prof. F.J. Murcray will be in charge of the University of Denver high-resolution interferometer, Prof. James R. Drummond will be the liaison between him and the other Canadian investigators. Prof. J.C. McConnell will not be directly involved with the instruments, but will advise on scientific issues that arise and that may have implications for the later modelling and interpretation of the data, for which he will have prime responsibility

As all of the instruments are either assembled or under construction, no instrument development will be required. The principal pre-launch activity relating to the instruments will be the calibration, and responsibility for this task will lie with the team members as discussed in the previous paragraph. There are four major pre-launch tasks to be completed, none of which is directly related to the scientific payload. The first is the development of a differential GPS system, and this will be managed by Dr. C.T. McElroy at AES. The remaining three tasks will all be handled by SIL, as they relate to the balloon and gondola; they are refurbishment of the azimuth control, modification of the tilting table feedback to allow both sun tracking and free scanning, and design of a gondola to carry both the tilting table and the high-resolution spectrometer.

Costs will be controlled through the University of Toronto, which will manage the contract with CSA. A Research Associate position will be partly employed for day-to-day management of the program under the direction of the PI (K. Strong), including management of the sub-contract to SIL. Project management software will be used to track progress against the required schedule.

References

Beagley, S.R., J. de Grandpre, J.N. Koshyk, N.A. McFarlane, and T.G. Shepherd, The First-Generation Canadian Middle Atmosphere Model, submitted to Atmos. Ocean, August, 1996.

Bojkov, R.D., L. Bishop, W.J. Hill, G.C. Reinsel, and G.C. Tiao, A Statistical Trend Analysis of Revised Dobson Total Ozone Data Over the Northern Hemisphere, J. Geophys. Res., 95, 9785, 1990.

Bloxam, R.M., A.W. Brewer, and C.T. McElroy, NO₂ Measurements by Absorption Spectrophotometer: Observations from the Ground and High Altitude Balloon, Churchill, Manitoba, Proc. Fourth Conf. Climatic Impact Assess. Prog., Cambridge, MA, DOT-TSC-75-38, 454, 1975.

Brewer, A.W., C.T. McElroy and J.B. Kerr, Nitrogen Dioxide Concentrations in the Atmosphere, Nature, 246, 129, 1973.

Chartrand, D.J, and J.C. McConnell, Heterogeneous Bromine Chemistry and the O₃ Budget in the Lower Mid-Latitude Stratosphere, to be submitted to J. Geophys. Res., January, 1997.

Crutzen, P., The Influence of Nitrogen Oxides on the Atmospheric Ozone Content, Quart. J. Roy. Meteorol. Soc., 96, 320, 1970.

Danilin, M.Y., and J.C. McConnell, Stratospheric Effects of Bromine Activation on/in Sulfate Aerosol, J. Geophys. Res., 100, 11237, 1995.

Davis, P.A., Observation of the Second Umkehr, M.Sc. Thesis, University of Toronto, 1972.

de Grandpre, J., J.W. Sandilands, J.C. McConnell, S.R. Beagley, P. Croteau, M.Y. Danilin, Chemistry in the Canadian Middle Atmosphere Climate Model, to be submitted to Atmos. Ocean, January, 1997.

DeMore, W.B., S.P. Sander, D.M. Golden, R.F. Hampson, M.J. Kurylo, C.J. Howard, A.R. Ravishankara, C.E. Kolb, M.J. Molina, Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling, JPL Publication 94-26, Pasadena, CA, 1994.

Dobson, G.M.B., Observer's Handbook for the O₃ Spectrophotometer, Ann. int. geophys. Year, 5, 46, 1957.

Dobson, G.M.B. and D.N. Harrison, Measurements of the Amount of Ozone in the Earth's Atmosphere and Its Relation to Other Geophysical Conditions, Proc. R. Soc., A110, 660, 1926.

Drummond, J.R., Radiometric Investigations of Traces Gases in the Atmosphere, D.Phil. Thesis, University of Oxford, 1977.

Drummond, J.R. and R.F. Jarnot, Infra-red Measurements of Stratospheric Composition II. Simultaneous NO and NO₂ Measurements, Proc. Roy. Soc. (Lond.), A364, 237, 1978.

Evans, W.F.J., J.B. Kerr, D.I. Wardle, J.C. McConnell, B.A. Ridley, and H.I. Schiff, Intercomparison of NO, NO₂, and HNO₃ Measurements with Photochemical Theory, Atmosphere, 14, 189, 1976.

Evans, W.F.J., J.B. Kerr, C.T. McElroy, R.S. O'Brien, B.A. Ridley, and D.I. Wardle, The Odd Nitrogen Mixing Ratio in the Stratosphere, Geophys. Res. Lett., 4, 235, 1977.

Evans, W.F.J., C.T. McElroy, J.B. Kerr, and J.C. McConnell, Simulation of Nitrogen Constituent Measurements from the August 28, 1976 Stratoprobe III Flight, J. Geophys. Res., 86, 12066, 1981.

Evans, W.F.J., C.T. McElroy, J.B. Kerr, and J.C. McConnell, Simulation of the October 23, 1980 Stratoprobe Flight, Geophys. Res. Lett., 9, 223, 1982a.

Evans, W.F.J., J.B. Kerr, C.T. McElroy, R.S. O'Brien, and J.C. McConnell, Measurements of NO₂ and HNO₃ During a Stratospheric Warming at 54 N in February 1979, Geophys. Res. Lett., 9, 493, 1982b.

Evans, W.F.J., C.T. McElroy, and I.E. Galbally, The Conversion of N₂O₅ to HNO₃ at High Latitudes in Winter, Geophys. Res. Lett., 12, 825, 1985.

Farman, J.C., B.G. Gardiner, and J.D. Shanklin, Large Losses of Total Ozone in Antarctica Reveal Seasonal ClO_x/NO_x Interaction, Nature, 315, 207, 1985.

Fish, D.J., R.L. Jones, and E.K. Strong, Midlatitude Observations of the Diurnal Variation of Stratospheric BrO, J. Geophys. Res., 100, 18863, 1995.

Gille, J.C. and J.M. Russell III, The Limb Infrared Monitor of the Stratosphere: Experiment Description, Performance and Results, J. Geophys. Res., 89, 5125, 1984.

Goldman, A., C.P. Rinsland, F.J. Murcray, F.H. Murcray and D.G. Murcray, Measurements of Several Atmospheric Gases Above the South Pole in December 1986 from High Resolution 3-4 Micron Solar Spectra, J. Geophys. Res., 93, 7069, 1988.

Goutail, F., J.P. Pommereau, and A. Sarkissian, Four Years of Ground-Based Total Ozone Measurements by Visible Spectrometry in Antarctica, Proc. Quad. Ozone Symp., Charlottesville VA, June, 1992, NASA Conf. Publ. 3266, 1994.

Hofmann, D., S.J. Oltmans, W.D. Komhyr, J.M. Harris, J.A. Lathrop, A.O. Langford, T. Deshler, B.J. Johnson, A. Torres, and W.A. Matthews, Ozone Loss in the Lower Stratosphere over the United States in 1992-1993: Evidence for Heterogenous Chemistry on the Pinatubo Aerosol, Geophys. Res. Lett., 21, 65, 1994.

Hofmann, D., P. Bonasoni, M. De Maziere, F. Evangelisti, G. Giovanelli, A. Goldman, F. Goutail, J. Harder, R. Jakoubek, P. Johnston, J. Kerr, W.A. Matthews, T. McElroy, R. McKenzie, G. Mount, U. Platt, J.-P. Pommereau, A. Sarkissian, P. Simon, S. Solomon, J. Stutz, A. Thomas, M. Van Roozendael, and E. Wu, Intercomparison of UV/Visible Spectrometers for Measurements of Stratospheric NO₂ for the Network for the Detection of Stratospheric Change, J. Geophys. Res., 100, 16765, 1995.

Kawa, S.R., J.B. Kumer, A.R. Douglass, A.E. Roche, S.E. Smith, F.W. Taylor, and D.J. Allen, Missing Chemistry of Reactive Nitrogen in the Upper Stratospheric Polar Winter, Geophys. Res. Lett., 22, 2629, 1995.

Kerr, J.B., Trends in Total Ozone at Toronto Between 1960 and 1991, J. Geophys. Res., 96, 20703, 1991.

Kerr, J.B., and C.T. McElroy, Measurement of Atmospheric Nitrogen Dioxide from the AES Stratospheric Balloon Program, Atmosphere, 14, 166, 1976.

Kerr, J.B., and C.T. McElroy, Evidence for Large Upward Trends of Ultraviolet-B Radiation Linked to Ozone Depletion, Science, 262, 1032, 1993.

Kerr, J.B., C.T. McElroy, and W.F.J. Evans, Midlatitude Summertime Measurements of Stratospheric NO₂, Can. J. Phys., 60, 196, 1982.

Kerr, J.B., D.I. Wardle, and D.W. Tarasick, Record Low Ozone Values over Canada in Early 1993, Geophys. Res. Lett., 20, 1979, 1993.

Lary, D.J., M.P. Chipperfield, R. Toumi, and T.M. Tenton, Heterogeneous Atmospheric Bromine Chemistry, J. Geophys. Res., 101, 1489, 1996.

McCormick, M.P., R.E. Veiga, and W.P. Chu, Stratospheric Ozone Profile and Total Ozone Trends Derived from SAGE I and SAGE II Data, Geophys. Res. Lett., 19, 269, 1992.

McElroy, C.T., Spectrographic Measurement of Atmospheric Nitrogen Dioxide, M.Sc. Thesis, University of Toronto, 1976.

McElroy, C.T., The Determination of Stratospheric Nitrogen Dioxide Concentrations from Limb Brightness Measurements made from a Balloon Platform, Ph.D. Thesis, York University, 1984.

McElroy, C.T., The Determination of Stratospheric Nitrogen Dioxide Concentrations from Limb Brightness Measurements, Proc. Quad. Ozone Symp., Halkidiki, Greece, C. Zeferos and A. Ghazi (eds.), D. Reidel, Hingham, MA, 222, 1985.

McElroy, C.T., Stratospheric Nitrogen Dioxide Concentrations as Determined from Limb Brightness Measurements Made on June 17, 1983, J. Geophys. Res., 93, 7075, 1988.

McElroy, C.T., A Spectroradiometer for the Measurement of Direct and Scattered Solar Spectral Irradiance from On-Board the NASA ER-2 High-Altitude Research Aircraft, Geophys. Res. Lett., 22, 1361, 1995.

McElroy, C.T. and D.I. Wardle, The Detection of OH and ClO in UV Spectra of the Sky and Sun Measured by a Balloon-Borne High Resolution Spectrometer, Proc. WMO Symposium on the Geophysical Aspects and Consequences of Changes in the Composition of the Stratosphere, WMO No. 511, 85, 1978.

McElroy C.T., J.B. Kerr, L.J.B. McArthur, D.I. Wardle, and D. Tarasick, SPEAM-II Experiment for the Measurement of NO₂, O₃ and Aerosols, in Ozone in the Troposphere and Stratosphere, Proc. Quad. Ozone Symp., Charlottesville VA, June, 1992, NASA Conf. Publ. 3266, 891, 1994.

McElroy, C.T., C. Midwinter, D.V. Barton, and R.B. Hall, A Comparison of J-values Estimated by the Composition and Photodissociative Flux Measurement with Model Calculations, Geophys. Res. Lett., 22, 1365, 1995.

McKenzie, R.L., P.V. Johnston, C.T. McElroy, J.B. Kerr, and S. Solomon, Altitude Distributions of Stratospheric Constituents from Ground-Based Measurements at Twilight. J. Geophys. Res., 96, 15499, 1991.

McLinden, C.A., J.C. McConnell, E. Griffioen, and C.T. McElroy, Sensitivity of Polarized Limb Radiances to Stratospheric Aerosols with Application to NASA ER-2 Spectrometer Measurements, in press, Proc. Quad. Ozone Symp., Aquila, Italy, September, 1996.

Molina, M.J., and F.S. Rowland, Stratospheric Sink for Chlorofluormethanes: Chlorine Atomic-Catalysed Destruction of Ozone, Nature, 249, 810, 1974.

Murcray, D.G., Trace Gas Measurements in the Stratosphere using Balloon-Borne Instruments, Rev. of Geophys., 25, 494, 1987.

Murcray, F.J., F.H. Murcray, C.P. Rinsland, A. Goldman and D.G. Murcray, Infrared Measurements of Several Nitrogen Species Above the South Pole in December 1980 and November-December 1986, J. Geophys. Res., 92, 13373, 1987.

Noxon, J.F., Nitrogen Dioxide in the Stratosphere and Troposphere Measured by Ground-Based Absorption Spectroscopy, Science, 189, 547, 1975.

Noxon, J.F., Stratospheric NO₂ in the Antarctic Winter, Geophys. Res. Lett., 5, 1021, 1978.

Noxon, J.F., Stratospheric NO₂. 2. Global Behaviour, J. Geophys. Res., 84, 5067, 1979.

Noxon, J.F., E.C. Whipple, Jr., and R.S. Hyde, Stratospheric NO₂. 1. Observational Method and Behaviour at Mid-Latitude, J. Geophys. Res., 84, 5047, 1979.

Pick, D.R. and J.T. Houghton, Measurements of Atmospheric Infrared Emission with a Balloon-Borne Multifilter Radiometer, Quart. J. Roy. Meteorol. Soc., 95, 535, 1969.

Preston, K.E., The Retrieval of NO₂ Vertical Profiles from Ground-Based Twilight UV-Visible Absorption Measurements, Ph.D. Thesis, University of Cambridge, 1995.

Ridley, B.A., Son Ha Luu, D.R. Hastie, H.I Schiff, J.C. McConnell, W.F.J. Evans, C.T. McElroy, J.B. Kerr, H. Fast, and R.S. O'Brien, Stratospheric Odd Nitrogen: Measurements of HNO₃, NO, NO₂, and O₃ near 54 in Winter, J. Geophys. Res., 89, 4797, 1984.

Rodgers, C.D., Retrieval of Atmospheric Temperature and Composition from Remote Measurements of Thermal Radiation, Rev. Geophys. Space Phys., 14, 609, 1976.

Rodgers, C.D., Characterization and Error Analysis of Profiles Retrieved from Remote Sounding Measurements, J. Geophys. Res., 95, 5587, 1990.

Roscoe, H.K., J.R. Drummond, and R.F. Jarnot, Infrared Measurements of Stratospheric Composition III. The Daytime Changes of NO and NO₂, Proc. Roy. Soc. (Lond.), A375, 507, 1981.

Roscoe, H.K., B.J. Kerridge, S. Pollitt, M. Bangham, N. Louisnard, J.-P. Pommereau, T. Ogawa, N. Iwagami, M.T. Coffey, W. Mankin, J.M. Flaud, F.J. Murcray, A. Goldman, W.F.J. Evans, and T. McElroy, Intercomparison of Stratospheric Measurements of NO and NO₂, Proc. Quad. Ozone Symp., Halkidiki, Greece, C. Zeferos and A. Ghazi (eds.), D. Reidel, Hingham, 149, 1985.

Roscoe, H.K., B.J. Kerridge, S. Pollitt, N. Louisnard, J.M. Flaud, C. Camy-Peyret, C. Alamichel, J.-P. Pommereau, T. Ogawa, N. Iwagami, M.T. Coffey, W. Mankin, W.F.J. Evans, C.T. McElroy, and J. Kerr, Intercomparison of Remote Measurements of Stratospheric NO and NO₂, J. Atmos. Chem., 10, 111, 1990.

Salawitch, R.J., et al. (36 co-authors), The Diurnal Variation of Hydrogen, Nitrogen, and Chlorine Radicals: Implications for the Heterogeneous Production of HNO₂, Geophys. Res. Lett., 21, 2551, 1994.

Sanders, R.W., Solomon, S., M.A. Carroll, and A.L. Schmeltekopf, Visible and Ultraviolet Spectroscopy at McMurdo Station, Antarctica, 4, Overview and Daily Measurements of NO₂, O₃, and OClO During 1987, J. Geophys. Res., 94, 11381, 1989.

Sandilands, J.W. and J.C. McConnell, Evaluation of a Reduced-Jacobian Numerical Chemical Solver, submitted to J. Geophys. Res., April, 1996, replied to reviewers, November, 1996.

Sandilands, J.W.; L. Neary, H. Ritchie, J.C. McConnell, J.W. Kaminski, Developing an Interactive Chemistry Solver for Inclusion with SEF, The Canadian Global Weather Forecast Model, CMOS Congress, Toronto, June, 1996.

Shepherd, T.G., The Canadian MAM Project, CMOS Bull., 23, 3, 1995.

Solomon, S., R.W. Sanders, M.A. Carroll, and A.L. Schmeltekopf, Visible and Ultraviolet Spectroscopy at McMurdo Station, Antarctica, 5, Observations of the Diurnal Variations of BrO and OClO, J. Geophys. Res., 94, 11393, 1989.

Solomon, S., A.L. Schmeltekopf, and R.W. Sanders, On the Interpretation of Zenith Sky Absorption Measurements, J. Geophys. Res., 92, 8311, 1987.

Stolarski, R.S., P. Bloomfield, R.D. McPeters, and J.R. Herman, Total Ozone Trends Deduced from Nimbus 7 TOMS Data, Geophys. Res. Lett., 18, 1015, 1991.

Stolarski, R.S., R. Bojkov, L. Bishop, C. Zeferos, J. Staehelin, and J. Zawodny, Measured Trends in Stratospheric Ozone, Science, 256, 342, 1992.

Strong, K. and R.L. Jones. Remote Measurements of Vertical Profiles of Atmospheric Constituents Using a UV-Visible Ranging Spectrometer. Applied Optics, 34, 6223, 1995.

Thompson, A.M., R.R. Friedl, H.L. Wesoky, (eds.), Atmospheric Effects of Aviation: First Report of the Subsonic Assessment Program, NASA Ref. Publ. 1385, May, 1996.

Torr, D.G., M.G. Torr, W. Swift, J. Fennelly, and G. Liu, Measurement of OH(X2) by High Resolution Spectroscopy, Geophys. Res. Lett., 14, 937, 1987.

Wahner, A. and C. Schiller, Twilight Variation of Vertical Column Abundances of OClO and BrO in the North Polar Region, J. Geophys. Res., 97, 8047, 1992.

Webster, C.R., R.D. May, R. Toumi, and J. Pyle, Active Nitrogen Partitioning and the Nighttime Formation of N₂O₅ in the Stratosphere: Simultaneous In-Situ Measurements of NO, NO₂, HNO₃, O₃, H₂O, and jNO₂ Using the BLISS Diode Laser Spectrometer, J. Geophys. Res., 95, 13851, 1990.

World Meteorological Organization, Global Ozone Research and Monitoring Project - Report No. 18, Scientific Assessment of Ozone Depletion, WMO, Geneva, Switzerland, 1991.

World Meteorological Organization, Global Ozone Research and Monitoring Project - Report No. 37, Scientific Assessment of Ozone Depletion: 1994, WMO, Geneva, Switzerland, 1995.

Appendix A. MANTRA Phase Two: A Second Balloon Flight

The primary focus of the MANTRA project is a single balloon flight to take place in August, 1998 at Vanscoy, Saskatchewan (52 N), in order to investigate long-term trends in the odd-nitrogen budget of the stratosphere and their possible role in explaining the anomalously large ozone depletion which has been observed at mid-latitudes during the last two decades. However, some thought has also been given to a second flight to occur one year later, as a successful initial flight of the instrument suite would prove its suitability for additional measurements at higher latitudes. A second flight would enable an investigation of the latitude-dependence of the odd-nitrogen chemistry. The exact flight plan would require careful planning, given the constraints imposed by the availability of sites in northern Canada, the logistics (assuming limited resources), and weather. This second phase of the MANTRA project could lead to highly desirable and extremely useful wintertime flights at high latitudes, possibly long-duration events using new technology, in conjunction with wintertime efforts of other nations. In particular, an opportunity to collaborate with a planned 1999 NASA campaign involving an ER-2 flight in the Arctic and validation of the SAGE-III satellite instrument has been identified.

If a second balloon flight does proceed one year after the first launch, a reduced version of the schedule for Phase One will be followed, as outlined in Table A.1. The Requirements Review and Preliminary Design Review will not be required, as the instrument payload will remain the same. The Critical Design Review will again be held six months before launch (February 1, 1999), at which point, any changes arising from lessons learned during the first flight will be finalized. The Flight Readiness Review will occur at the same time as the Second Data Workshop, 4 weeks before the second launch (July 1, 1999), and shipping and integration will begin two weeks before launch (July 15, 1999). Launch will again be scheduled take place as close as possible to August 1, 1999. The schedule for post-flight data, reports, and workshops will follow the same pattern as for the first balloon flight.

Table A.1. Program schedule and milestones for MANTRA Phase Two.