Sp-461 ers-envisat Symposium

GAIN CALIBRATION

Objectives

The purpose of the ASAR gain calibration is to provide the users of ASAR data with the possibility to determine the

absolute level of backscatter from any target, point (sigma) or distributed (sigma zero). For ASAR this is achieved in

fundamentally the same way as for ERS, namely by providing an Absolute gain Calibration Factor (ACF) in the header

of the (processed) product. Since ASAR, however, has a total of eight beams and five different modes and up to four

Figure 3 : FM Elevation Beam Pattern Measurement

Figure 4 : FM Azimuth Beam Pattern Measurement

Figure 5 : ERS-2 Image over the Rain

Forest without Antenna Pattern

Correction

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polarizations many more ACFs will need to be determined for ASAR than was the case for ERS with its single beam,

single polarization and two modes. This is summarized in table 1.