Differences of Sar Image Between JERS-L and
ERS-L To Land Use/Land Cover Investigation
JERS-l SAR image acquired on 25 June 1992, path-row 127-277 and 127-278 resampling pitch 12.5 m, altitude 568 km, beam direction 35°, frequency 1275 MHz (L band) and ERS-1 SAR image acquired on 10 August 1993, path-row 10684-3321 and 10684-3339, resampling pitch 12.5 m, altitude 785 km, beam direction 23°, frequency 5.3 Ghz (C band), polarization VV, spatial resolution 30 m, swath 100 km were visually analyzed. Topographic maps on a scale of 1:50,000 and OPS image (IB 30 2R) of JERS-l of the same area were used in ground truth. From visual interpretation of SAR image and field observation, it was found that parameters which mainly influence differences of backscatters in SAR image from JERS-1 and ERS-1 are orientation of objects, vegetation height or object height and incidence angle.
Orientation of object is directly related to look direction. When the orientation of object is perpendicular to look direction, backscatters will be very strong. On the other hand backscatter will be very low when orientation of object is parallel to look direction.
Vegetation height or object height is one of the parameter which cause difference in backscatter. When object height is more than 30 cm backscatter in SAR image from ERS-1 will be strong while SAR image from JERS-1 will be very low backscatter. So weed and grass with 30 cm height can be observed by ERS-l better than JERS-l. Incidence angle has an effect in urban and
built up land. In Thailand most of the angle of roof pitch are approximately 20 o , backscatter to
ERS-1 is stronger than JERS-1.
Conclusion and Recommendation
There are tree main parameters influencing the backscatters from land use/land cover, they are orientation of object, vegetation height or object height and incidence angle. Urban area identification is easier ERS-1 SAR than JERS -1 image but some area it will be more clear from .JERS-1 SAR image if object orientation is perpendicular to look direction. In agriculture land, backscatter will be stronger in ERS-1 image than JERS-1 SAR image, especially when vegetation height is less than 30 cm.
To use only SAR data to identify land use type, the result is not satisfied. To get best result, it is recommended to use SAR data together with other data from passive remote sensing system and also Geographic Information System.
This project was funded by the Science and Technology Agency (ST A). This support was greatly appreciated.
Shunji Murai; Remote Sensing Note, JERS -1 1993
- Rob Schuman; Microwave Remote Sensing, ESA, 1994.
- B.N. Koopmans; Side looking Radar, ITC, 1991
- Valairat Wanpiyarat; Synthetic Aperture Radar Image Interpretation annual Development Thailand Area GSI 1994 .
- Wirat Thongs; Land use analysis by using remote sensing data, GSI 1993.