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| Titel |
MIRAS characterization and monitoring during the SMOS In-Orbit Commissioning Phase |
| VerfasserIn |
I. Corbella, F. Torres, M. Martin-Neira, N. Duffo, V. González-Gambau, A. Camps, M. Vall-llossera |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250025059
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| Zusammenfassung |
| 1 Introduction
The Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) is the single payload
of the Soil Moisture and Ocean Salinity (SMOS) mission. The instrument was completed in
early 2007 and thoroughly tested both in anechoic chamber and vacuum thermal chamber
during 2007. It was integrated to the platform in early 2008 and re-tested, including
compatibility, during 2008. At present, the whole satellite is stowed and waiting to be
launched during 2009.
In two weeks after launch, the satellite will be in the final orbit with all deployments
completed. Then the In-Orbit Commissioning Phase will start, having an estimated duration
of 5.5 months. During this phase, the instrument modes of operation will be systematically
checked and the calibration parameters will be fully characterized in real conditions. Also,
the first brightness temperature images will be obtained in order to assess the overall retrieval
procedures including inversion. In the end, the objective of the In-Orbit Commissioning
Phase is to provide verification that the payload meets the scientific requirements of the
mission.
The general design and planning of the In-Orbit Commissioning Phase is given in [1].
This abstract presents the foreseen activities to be performed during this phase by the UPC
team.
Just after the start of the In-Orbit Commissioning Phase, the instrument will be
commanded to perform a sequence of operations oriented at providing a full characterization
in terms of calibration parameters. The idea is to reproduce the results obtained
during the tests carried out on ground [2]. In particular, the following issues will be
covered:
Thermal Stability: To provide understanding of both the intra-orbit and inter-orbit
temperature variations. The instrument will be continuously operating during a
number of orbits while all temperature sensors being monitored.
Electrical Stability: To re-compute all internal calibration parameters (gains, offsets,
receiver noise temperatures, visibility phases and G-matrix elements) and assess
about their stability and temperature dependance. The sensitivity coefficients for
these parameters will be computed, compared with the ones obtained on ground
and used to feed the calibration data base for further use in nominal operation.
Absolute amplitude calibration: Obtained by measuring the brightness temperature
of a known target using the reference Noise Injection Radiometer (NIR). The
satellite attitude will change so that it will point to the deep sky with known
brightness temperature.
Flat Target Response: That is, the visibility corresponding to a target with unit
brightness temperature from all directions [3]. This is an important parameter for
inversion and will be obtained also with the satellite pointing to the deep sky.
2 Imaging
Once the instrument fully characterized, a continuous set of orbits will provide
observation data to allow processing to higher levels and to provide brightness
temperature maps of selected zones of the Earth. Two modes of operations will be
considered
Dual-polarization operation: In this mode the brightness temperature at two
orthogonal polarizations will be obtained after inversion of the corresponding
visibility measurements. Since the objective of this processing is to assess about
inversion methods and algorithms, the reference frame used will be the one
defined by the instrument.
Full-polarimetric operation This mode provides the four Stokes parameters of the
Earth emission
citepolmiras. Although in principle, this is not the nominal mode of operation,
the commissioning phase provides an opportunity to test this mode and compare
the results with the dual-polarization mode.
3 Data processing
The data will be processed with the MIRAS Testing Software (MIRAS-TS), a tool
specifically developed by UPC to test the payload operation [5]. It was successfully used
during the on-ground characterization of the instrument [2] and it is now being updated in
order to be efficiently used for the in-orbit commissioning phase.
The tool can ingest raw data from the electronic ground support equipment (EGSE)
developed by the instrument manufacturer and also from the nominal level 0 data provided by
the SMOS ground segment data acquisition system. The software classifies the input data and
applies the calibration procedures to produce calibrated visibility and brightness
temperature. Most of the intermediate results, including raw data and calibration
parameters, are saved in files for further analysis and processing. The processing has
been optimized for speed so that the results are produced in near real time and
it is designed to process large amount of data in a continuous way. Finally, the
tool includes a user-friendly graphics interface that allows selecting specific data
according to different parameters (baselines or receivers, modes of operation or
others).
4 Conclusions
During the SMOS In-Orbit Commissioning Phase, a number of tests will be carried out in
order to check the payload MIRAS operation and fully characterize it in terms of data
consistency and calibration parameters. The UPC team is in charge of analyzing the data and
develop the procedures to verify that the final data meets the required specifications. The
procedures for this have been summarized and will be presented at the conference in more
detail.
References
[1]Â Â Â Michael Brown, “SMOS in-orbit commissioning phase plan,” Tech. Rep.
SO-PL-ESA-SYS-5505, issue 1.1, ESA-ESTEC, The Netherlands, 8 August
2008.
[2]Â Â Â Ignasi Corbella, Francesc Torres, Nuria Duffo, Manuel Martín-Neira,
Verónica González, Adriano Camps, and Mercè Vall-llossera, “MIRAS ground
characterization,” in 10th Specialist Meeting on Microwave Radiometry and
Remote Sensing of the Environment - μRad 2008, Florence, Italy, 11-14 March
2008, Istituto di Fisica Applicata “N.Carrara” (IFAC-CNR), pp. 1–4.
[3]Â Â Â Manuel Martín-Neira, Martin Suess, and Juha Kainulainen, “The flat target
transformation,” IEEE Transactions on Geoscience and Remote Sensing, vol. 46,
no. 3, pp. 613–620, March 2008.
[4]Â Â Â Manuel
Martín-Neira, Serni Ribó, and Arturo J. Martín-Polegre, “Polarimetric mode of
MIRAS,” IEEE Transactions on Geoscience and Remote Sensing, vol. 40, no. 8,
pp. 1755 –1768, August 2002.
[5]Â Â Â Ignasi Corbella, Francesc Torres, Nuria Duffo, Verónica González-Gambau,
Adriano Camps, and Mercè Vall-llossera, “Fast processing tool for SMOS
data,” in International Geoscience and Remote Sensing Symposium, IGARSS 2008,
Boston(Ma), USA, 7 - 11 July 2008, IEEE. |
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