Interferometic synthesis aperture radiometer calibration fundamentals and error budget.

Paper number

IAC-06-B1.P.1.13

Author

Mrs. Ana Olea, EADS CASA Espacio, Spain

Coauthor

Mr. Andres Borges, EADS CASA Espacio, Spain

Coauthor

Mr. Andrés Solana, EADS CASA Espacio, Spain

Coauthor

Mr. Carlos Garcia, EADS CASA Espacio, Spain

Coauthor

Mr. Adriano Camps, Universitat Politecnica de Catalunya, Spain

Coauthor

Mr. Ignasi Corbella, Universitat Politecnica de Catalunya, Spain

Year

2006

Abstract

An interferometric aperture synthesis radiometer, such as SMOS, needs the careful definition of appropriate parameters to measure its radiometric performance. 

Unlike a real aperture radiometer, interferometric radiometer requires an internal relative error correction of each visibility sample, in order to avoid image aberration an after that, an external absolute calibration is needed. Since SMOS  is a new radiometer concept a totally innovative calibration methods are associated to it. 

When the instrument points to a given brightness temperature map the retrieved image obtained after processing and reconstructing the raw data is different than the original map, therefore an error is produced and simple figures to characterize this error are needed. 

The fundamentals which calibration procedure are based could be divided into two categories, the instrumental errors correction and the in-orbit calibration and error budget. 
The instrumental errors correction is a set of measurement procedures and mathematical relations that allow the user to remove instrumental errors.  In order to deal with this undesired corruption of the measured signal, the instrument is characterized by the error model. 
The error model of the instrument characterizes its behaviour independently of the signal at its input. Therefore, by means of suitable internal known signals injected at its input this undesired corruption can be characterized and eliminated  from the measured magnitudes. The image just after calibration gives the best instrument resolution, this image is compared with a reference image for the error computation and two error figures are computed for this image:  Radiometric sensitivity related to a random error, and radiometric accuracy and radiometric bias related to a systematic error.

The in-orbit calibration procedure is useful to give an error budget that relates system and subsystem specifications to radiometric accuracy. Hence,  the optimum error budget is only valid for the measurements that are performed just after the calibration sequence since instrument parameters drift apart from the calibrated value due to two main factors, temperature drift and aging , as well as  internal interference.  

The validation of system performance and error budget is also possible by means of a testing software (SEPS) developed with this purpose. 

Abstract document

IAC-06-B1.P.1.13.pdf

Manuscript document

IAC-06-B1.P.1.13.pdf (🔒 authorized access only).

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