373 
of the ERS-1 system including the processors. (-) in Table 1 means that the target has not been 
imaged on that particular orbit, (*) means that the plates of the reflector were snow-covered. On 
March 8 only three and on November 24 only two of the six reflectors have been cleared from snow. 
Snow on the plates reduces the RCS by up to 20dB. 
With the exception of orbit 11833 all RCS values of the different reflectors are in good 
agreement with each other (min-max variation is less than ldB) and also with the theoretical value. 
The average value tends to slightly higher radar cross sections them the theoretical one. That 
consequently means that ESA’s calibration factor is too low by a few tenth of a dB. Detailed analysis 
indicates differences of data processed by the UK and German PAF. This offset in the calibration 
of data from different PAFs and the lower RCS values from orbit 11833 are under investigation. 
Date 
Orbit 
CR 1 
CR 2 
CR 3 
CR 4 
CR 5 
CR 6 
13-01-93 
7825 
51.1 
50.1 
50.6 
50.8 
50.7 
50.6 
01-02-93 
8097 
50.5 
50.0 
50.9 
50.7 
50.7 
50.6 
17-02-93 
8326 
- 
- 
47.1* 
47.6* 
- 
44.8* 
08-03-93 
8598 
50.2 
50.3 
46.9* 
45.2* 
34.9* 
49.8 
12-04-93 
9099 
50.6 
50.5 
50.4 
50.5 
50.4 
50.6 
28-04-93 
9328 
50.9 
50.7 
50.8 
50.8 
50.7 
50.7 
17-05-93 
9600 
49.8 
50.0 
50.0 
50.0 
50.0 
50.0 
02-06-93 
9829 
50.9 
50.2 
50.6 
50.9 
50.7 
50.7 
21-06-93 
10101 
50.0 
50.3 
50.1 
49.8 
49.9 
50.2 
07-07-93 
10330 
- 
- 
50.3 
50.2 
- 
50.5 
26-07-93 
10602 
50.9 
50.8 
50.4 
50.6 
50.5 
50.5 
11-08-93 
10831 
- 
- 
50.5 
50.1 
- 
50.3 
30-08-93 
11103 
50.0 
49.9 
50.0 
50.0 
50.0 
50.0 
15-09-93 
11332 
- 
- 
50.5 
50.6 
- 
50.3 
04-10-93 
11604 
50.0 
50.0 
49.8 
49.8 
50.1 
50.2 
20-10-93 
11833 
- 
- 
47.3 
47.5 
- 
47.5 
20-10-93 
11840 
51.0 
50.8 
51.0 
50.6 
51.3 
50.9 
08-11-93 
12105 
50.3 
50.6 
50.6 
50.6 
50.5 
50.4 
24-11-93 
12334 
- 
- 
50.3 
50.5 
- 
44.3* 
Table 1: RCS values of 3m corner reflectors measured by ERS-1. 
For future multichannel and multisensor remote sensing systems (e.g. SIR-C/X-SAR) it is 
desirable to be able to cross-calibrate data from different tracks and different sensors (channels). The 
1989 calibration campaign at the DLR test site in Oberpfaffenhofen [1] gave an opportunity for such 
an experiment, including a cross-calibration of the E-SAR and AIRSAR. Statements concerning the 
quality of cross-sensor calibration can be derived from the variation of the average backscattering 
coefficient in range direction. In order to achieve coincidence, the average a° values (derived from 
data of the same track) in Fig. 7 are plotted against the corresponding ground range position. 
The reference point is the position of a prototype PARC which was tested in that experiment. 
Both systems measured nearly the same backscatter except for near and far range. This is most 
probably due to the differences in incidence angles resulting from different flight altitudes of the 
two airplanes. An alternative explanation for the increased E-SAR values in this range could be 
the changed weather conditions: fight rain in the morning during the E-SAR flights, warm and 
sunny in the afternoon during the DC-8 flights. This indication is strengthened by the fact that 
the middle part in the cross-track direction is dominated by man-made structures and urban areas 
(DLR buildings and the village of Gilching) where the backscatter might be considered less sensitive 
to moisture. In these areas the measured backscatter is more nearly coincident.