MAMBO
Mars Atmosphere Microwave Brightness Observer
Reports from the Paris meeting (Feb., 4-6, 2002): Mambo science and design
DRAFT N°1
Rédigé par : date : visa : / Approuvé par : date : visa :F. Forget
LMD
IPSL
Université Pierre et Marie Curie, BP99,
4 place Jussieu 75252 Paris Cedex 05 / LERMA
Observatoire de Paris
61 av. de l'Observatoire,
75014 Paris
Réf. : MB.RP.IF.01.00.D1 / M A M B O / Date :February 21 2002
TABLE OF CONTENT
TABLE OF CONTENT 2
1. INTRODUCTION 3
2. SCIENCE REQUIREMENTS 3
Temperature and winds: (from F. Forget) 3
Science requirements for water vapor profiling 4
Science requirements for HDO (Þ DH ratio) measurements 5
Requirements on [CO] 5
Requirements on [O3] 5
Requirements on [H202] 5
3. SIMULATIONS OF INSTRUMENT PERFORMANCE AND INVERSIONS 5
Tools used 5
Results on Temperature and [H2O], [HDO], [O3], [H2O2] inversions 6
Results on Wind inversion 6
4. SURFACE SCIENCE 7
5. OBSERVATIONAL STRATEGY 7
6. MAMBO : DESIGN FOR SCIENCE 9
Antenna 9
Heterodyne Receiver and IF processor 10
Filters and spectrometers 11
On board data processing, data-rate and computer. 12
Mambo pre-launch calibration considerations 12
Science Ground segment 12
1. INTRODUCTION
A 3 days meeting about the Mars Atmosphere Microwave Brightness Observer was held in Paris on February 3, 4, 5 , 2002. Rather than "minutes" of the meeting, this report is a summary of the major points on which we agreed with regard to the science and the scientific aspect of the design of MAMBO.
At this stage, MAMBO is a limb + nadir heterodyne instrument using spectrometers to monitor the following lines :
•CO at 345,796GHz
•13CO at 330,588GHz
• H2O at 325,153GHz
•HDO at 335,395GHz
•O3 at 326.901 GHz
• H2O2 at 326,981 GHz
• In addition, 1 or 2 large filters dedicated to the measurement of the continuum (surface) are planned.
• The weaker H2O line at 321,226 GHz was considered to complement the stronger H2O, but finally not chosen (see below).
Temperature and wind measurements will be primarily performed using CO and 13CO
2. SCIENCE REQUIREMENTS
Temperature and winds:
Temp. & wind / Values / RationaleLatitudinal coverage / 0° to |lat| ³ 75° / Polar warming observations
Baroclinic Waves observations
Horizontal resolution / Ideal: Dlat £5°
(~100s on low orbit)
Descope: Dlat £10°
(~200s on low orbit) / Scale of free atmosphere structures
Catch main atmosphere characteristics
Vertical coverage / As high as possible
(up to 120 km) / Vertical Extension of meteorological phenomena in models. Truly new science to be performed above 70-80 km with the T measurements (previous instrument limited to z £ 70-80 km, although none will have observed winds at any altitude)
Local time coverage
· Ideal
· Descope (1)
· Descope (2) / Coverage of diurnal
cycle in £ 50 sols
‘ ‘ ‘ ‘£ 100 sols
A few fixed localtime / Mapping of diurnal cycle (tides) every Martian “months”
‘ ‘ ‘ every 1/6 of year
Keep information about time
Winds / Values / Rationale
Zonal or meridional
Winds ? :
· z 60 km
· z 60 km / Zonal
TBD / Weakness of meridional wind structures
Both of high interest
Accuracy / DU£15 m/s / Monitor mean flow + waves
Vertical resolution / Dz = 10 km / To be confirmed
T: Accuracy and Vertical resolution / Values / Rationale
General Circulation, Ideal: / DT =2K; Dz =10km / 3D circulation determination
(See MEPAG report and Haberle and Catling, PSS44, 1361-1383, 1996)
General Circulation,
Descope: / DT =5K; Dz =10km / Wave monitoring.
Local structures / DT =5K; Dz =5km / Local phenomena, clouds
Science requirements for water vapor profiling
Values / RationaleLatitudinal coverage / 0° to |lat| ³ 85° / Polar caps monitoring in summer
Horizontal resolution / Dlat £5° / Size of structures (clouds)
Vertical resolution / Dz £ 5 km / Monitoring of saturation level, etc.
Accuracy / £3% @ 10 km
£30%@ 40km
TBD / MEPAG (?)
MEPAG(?)
Detection of sources and sinks
Cloud formation in diurnal cycle
Etc…
Diurnal coverage / As for Temperature and winds or better / Key role of diurnal cycle
Science requirements for HDO (Þ DH ratio) measurements
Hability to monitor at least the Photo-dissociation induced Fractionation effect (Cheng et al. GRL 26, 3657-3660, 1999) or the Condensation-Evaporation Fractionation effect (e.g. Fouchet and Lellouch, Icarus 144, 114-123, 2000; Bertaux and Montmessin, JGR, in press 2002). These are possibly very strong effect (depletion of HDO vs H2O by a factor of 5 to 10 between 5 and 30 - 40 km
Þ [HDO] retrieval accuracy better than 50% at 30 – 40 km
Þ More work required on the subject.
Requirements on [CO]
· Requirements for Temperature retrieval : TBD
· Chemistry Science : Ability to monitor variations predicted in Joshi, Haberle and Clancy (unpublished preprint available)
Þ Variations : minimum accuracy 10-4 (Volume Mixing ratio) or 10% (To be confirmed)
Þ Vertical coverage : Strong interest for measuring CO as high as possible (120 km or above) to monitor the photochemical source. “Official requirements” to be determined
Requirements on [O3]
· Ability to map spatial, vertical, seasonal variations as simulated in various photochemical model (e.g. Clancy and Nair JGR 101, p12,785, 1996; other references available, see T. Clancy):
Þ Accuracy : 10-8 (Volume Mixing ratio), possibly 10-9 in some extreme cases (To be confirmed) between 0 and 40 km or possibly 60 km
Requirements on [H202]
· Never detected on Mars : innovative science is… easy ?
· According to models, mapping H2O2 variations should typically requires a sensitivity of 10-8 (Volume Mixing ratio) at 10 – 20 km (To be confirmed)
3. SIMULATIONS OF INSTRUMENT PERFORMANCE AND INVERSIONS
Tools used
· MOLIERE (Microwave Odin Line Estimation and Retrieval). Direct and Inversion tool (optimal estimation) developed at Bordeaux Observatory for the ODIN mission and adapted to Mars conditions for MAMBO (P. Ricaud, J. Urban; K. Dassas). This will be the main tool used to design MAMBO and the observing strategy.
· A similar tool may be available at MPAE (P. Hartogh)
· A direct + simple “Onion peelings” inversion tools developed by F. Forget for test in complement to MOLIERE
· Simplified scheme developed by M. Janssen, S. Gulkis ?
Results on Temperature and [H2O], [HDO], [O3], [H2O2] inversions
· A separate technical report gathering the simulations results presented at the Paris meeting written by Karin Dassas is (or will be soon) available.
· In Summary, preliminary studies suggest that
o MAMBO should be able to achieve most of the scientific requirements. However, to reach these requirements (including a latitudinal resolution better than 5°, corresponding to a total nadir+limb+calibration time under 100s), a system temperature close to 1500 K (DSB) or better is necessary.
o For temperature and [H2O], vertical resolution of 5 km should be possible at least in the lower atmosphere below 50 km.
o A bandwidth of 200 MHz is not sufficient to retrieve H2O accurately at low altitude in wet and even medium atmosphere. A larger bandwidth or adding “filters” on the line wings solves the problem, whereas adding a weak H2O line at 321 GHz did not seem very useful to improve the retrieval. Mike Janssen questioned this conclusion suggesting that we check any error in the weak line simulation. However, in terms of hardware and general performance, the “cost” of adding this line is not negligible so, at this stage, our baseline plan is to go without the H2O line at 321 GHz)
o In many cases a high spectral resolution is not necessary. 400 kHz or worse may often be sufficient (limit value TBD). Paul Hartogh remarks than, in theory, high spectral resolution is really useful for low noise, long integration studies(i.e. when averaging spectra). Tests performed after the meeting by Karin confirms that high spectral resolution (100 kHz) is indeed at least necessary to retrieve Temperature above 50 km (and to a less extend water above 40 km). Therefore 100 kHz resolution spectrometers should be used for line centers, but spectral binnning to lower the data rate should be used extensively.
· During the meeting, it was emphasized that to simulate the true performance of MAMBO, modelling the simultaneous inversion of Temperature and Mixing ratio was necessary (actions for the Moliere team).
Results on Wind inversion
Wind retrieval is not yet included in the Moliere tool. Preliminary work by Mike Janssen (a memo sent by E-mail on 06/06/2001 is available) and François Forget taking into account a realistic noise level (and perfect spectral calibration and baseline) both suggest that Doppler wind could retrieved with an accuracy better than 10 M/s (or even 5 m/s in these ideal calculations) over a wide range of altitude using CO and 13 CO. However, the altitude range differ in the two calculations (15-90 km for Forget, 30-120 for Janssen). This discrepancy must studied and understood in the future.
4. SURFACE SCIENCE
Catherine Prigent from LERMA, an expert of Earth surface remote sensing in the microwave presented some possible application of surface science that could be performed with MAMBO showing interesting terrestrial example. MAMBO should include a continuum channel able to measure the surface brightness temperature with a good accuracy. This measured brightness temperature Tb=eT differs from the skin surface kinetic temperature because 1) the emissivity e can be significantly lower than unity and 2) the temperature T sensed in the microwave reflect the vertically integrated physical temperature of the subsurface as weighted by the absorption coefficient of the regolith or ice material (MIME proposal), within the top cm of the Mars surface for dry soil or less if ice is present (To be confirmed).
However, a key problem to perform quantitative science with MAMBO surface (in the absence of simultaneous thermal measurements at other wavelengths) is to separate the variations of surface emissivity e from the actual ground temperature T. Nevertheless, interesting results may be obtained:
· The ground temperature on Mars can be modelled with a good accuracy (error £ 10 K) if the local surface, thermal inertia and atmospheric dust content is well estimated. The first two are already available with an increasing accuracy from the TES (and later Themis) observations. In such conditions, emissivity below 90% could be detected and variations of the order of 10% could be mapped. This may be especially true over the CO2 ice caps where the CO2 frost temperature only depends from the surface pressure and where low emissivity are expected (To be confirmed).
· It might be possible to measure a thermal inertia of the subsurface (a key parameters for Mars Science). Further work is required to understand if this thermal inertia will be of interest compared to the surface thermal inertia already measured in the IR
· As on Earth, it might be possible to learn more about the ground properties (roughness, physical properties) by comparing the surface emission observed in horizontal and vertical polarization. This might be possible in practice since we are now considering a double receiver to lower the noise (see below).
5. OBSERVATIONAL STRATEGY
Mike Janssen presented some results of a preliminary study (MAMBO observational scenario parameter study, viewgraphs available). Similar approach can be applied on the basis of the Moliere inversion results, although a dedicated study remains to be performed.
MAMBO antenna will alternatively look at
· The internal calibration load
· One or several points at Nadir (integration time per point : 1 – 5 s , TBC)
· The cold sky above the limb
· The limb (on one or both side).
A first key issue is the observations strategy at the limb. A few inputs :
· MAMBO antenna will be in constant rotation or rotate step by step (TBD). It will acquire spectra every 2 km or every 5 km (Every 2 km is better, but it may not be worth the increased complexity and data rate : to be decided on the basis of inversions simulations).
· The “rotation rate” of the antenna will correspond to a scanning of the vertical at 3±2km/s.
· In theory, limb scanning should be performed between 0 to 130±10 km (TBC). In practice, it may be necessary to take margins on both side (TBD). The strategy to “find” the limb on the basis of the information provided by the orbiter main CPU and/or from the detection of the limb by the instrument itself remains to be defined.
Orbiter altitude (km) / H / 170.0 / 350.0 / 500.0 / 1000.0Orbiter velocity (km/s) / V / 3.47 / 3.39 / 3.32 / 3.12
Distance Orbiter-limb at 0 km (km) / D (0) / 1086 / 1579 / 1907 / 2789
Distance Orbiter-limb at 130 km (km) / D(130) / 527. / 1252. / 1641. / 2601
Pointing angle (°) to the surface / q / 72.2 / 65.0 / 60.6 / 50.6
Limb (0-130 km) apparent angle (°) / Dq / 9.2 / 5.2 / 4.2 / 2.8
Limb scanning rate (km/s) / dz/dt / 3±2 / 3±2 / 3±2 / 3±2
Antenna mean rotation rate (°/s) / dq/dt / 0.21±0.14 / 0.12±0.08 / 0.10±0.06 / 0.06±0.04
Table summarizing the geometry of limb scanning for the various orbits considered in the CNES AO, with numbers illustrating the possible range of rotation rate for the antenna during limb scanning.