Sp-461 ers-envisat Symposium

Table 2: ASAR Performance Summary

Parameter

Unit

Image

Alternating

Polarisation

Wide

Swath

Global

Monitoring

Wave

Polarisation

-

VV or HH

VV/HH,

HH/HV,

or VV/VH

VV or HH

VV or HH

VV or HH

Spatial resolution (az. x ra.)

* except swath IS1

m

27.5 x 28.1*

28.7 x 29.7*

149 x 145

949 x 977

27.5 x 29.6 *

Radiometric Resolution

dB

1.54

2.46 to 2.50

1.45 to 1.72

1.35 to 1.44

1.54

Point Target Ambiguity Ratio

- azimuth

- range

dB

dB

25.9 to 29.6

31.6 to 45.8

19.1 to 28.0

26.4 to 40.5

22.3 to 28.6

25.0 to 33.9

26.6 to 29.3

25.0 to 32.2

27.3 to 29.6

31.2 to 45.7

Dist. Target Ambiguity Ratio

- azimuth

- range

dB

dB

22.6 to 24.7

17.1 to 39.4

18.1 to 24.5

17.1 to 39.4

20.3 to 24.9

17.1 to 30.8

24.6 to 27.5

17.1 to 30.8

22.6 to 24.7

21.2 to 47.7

Radiometric Stability (1

σ

)

dB

0.32 to 0.40

0.50 to 0.55

0.32 to 0.42

0.46 to 0.53

0.55 to 0.60

Radiometric Accuracy (3

σ

 )

dB

1.17 to 1.38

1.62 to 1.81

1.20 to 1.45

1.54 to 1.74

1.80 to 1.94

Noise Equivalent 

σ

0

dB

-19.6 to -22.1

-19.4 to -21.9

-20.9 to -26.2

-31.5 to –35.0

-19.8 to -22.4

Figure 9 : Interpolated SAR Impulse Response Function

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CONCLUSIONS

ASAR instrument calibration includes four major tasks: verification of in-flight temperature profiles, antenna pattern

determination, internal calibration and absolute calibration. In-flight temperature conditions will be verified during in-

orbit checkout for different operating profiles and monitored throughout the mission. Various in-flight measurements on

the active antenna will be combined with preflight characterization data in the antenna model. Monitoring of instrument

gain and phase variations will be performed regularly during data acquisitions using the calibration pulses. Absolute

calibration will rely on external reference targets.

Using a combination of precision calibration transponders and natural distributed targets the intention is to have the

Image, Wave (covered in a separate paper) and Wide Swath modes calibrated within six months of launch. With the

launch of ENVISAT less than a year away (scheduled for June 2000), the calibration plan for the ASAR is nearing

completion.

REFERENCES

[1] “ENVISAT ASAR Precision Transponders”, H Jackson ESA/ESTEC, I Sinclair, S Tam MPB Technologies Inc,

CEOS SAR Workshop 2-29 October 1999, ESA-SP450

[2] “The ENVISAT ASAR Instrument Verification and Characterization” R Torres, C Buck, J Guijarro, J-L Suchail,

A Schönenberg, ESA/ESTEC, CEOS SAR Workshop 2-29 October 1999, ESA-SP450

[3] “RADARSAT Precision Transponders”, R.K. Hawkins, et.al., Adv. Space Res. Vol. 19, No. 9, pp. 1455-1465, 1997.

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