Multi- Seasonal Analysis of SAR Data for Agriculture
Genya Saito, Nobuyuki Mino and Akira Hirano
Remote Sensing Laboratory,
National Institute of Agro-Environmental Sciences
Kannondai 3-1-1, Tsukuba, Ibaraki 305, Japan
Fax :+81-298-38-8199
E-mail : genya @niaes.affrc..go.jp,
hirano@niaes.affrc.go.jp
Abstract
Multi-seasonal analyses of SAR data for agriculture were performed using JERS-1(L-band DAR) and ERS-1 (C-band SAR) images at grassland, upland farming field and paddy area in Hokkaido, northern island in Japan.
In konsen-plateau in the north-eastern part of Hokkaido, which is comprised mainly of grassland ,images of JERS-1 data taken in April, June and August looked similar to each other except the spots where land use change occurred. In Tokachi plain, which is comprised mainly of upland farming field the back scattering coefficients of ERS-1 data taken in August are larger than those of April. In the same area. images of JERS-1data taken in June, August and October looked different from each other in agricultural field because of the soil-surface conditions. In Ishikari plain, which is comprised mainly of paddy, the back scattering coefficients of ERS-1 data taken in June when water fills the paddy are smaller than those of August and October when no water is in the paddy.
The JERS-1 microwaves pass through agricultural pants and then scatter at the ground surface, but ERS-I microwaves scatter at agricultural plants. Although we cannot get direct information about agricultural plants using JERS-1 data, we can get useful information about agricultural environment from the data. TheERS-1 SAR can directly measure agricultural crops, but the data include other information such as soil surface conditions and topographical features.
1.Introduction
Many studies on agriculture using remote sensing technique have been performed in Japan since LANDSAT was launched in 1972. these studies were made using optical sensors such as LANDSAT/TM MSS,SPOT/HRV, MOS/MESSR, and NOAA/AVHRR.
In Japan, crop growing period is from May to September, when temperature is relatively high and it rains much. It is very difficult to acquire optical remote sensing data during that time because of the cloud cover. Data acquisition is highly restricted in some tropical rainforest areas.
We use SAR data as the solution to the data acquisition problem, and to get other information concerning object size, form and water contents. Quantitative treatments to multi-temporal data can be performed , because same microwave energy reaches on earth every time when using same SAR instrument while data from optical sensors are greatly influenced by atmospheric conditions, SAR data are believed to be quite independent from atmospheric effects.
ERS-1 and JERS-1 were launched in 1991 and in 1992 respectively, and both satellites have SAR instruments. In Europe and America, there are some experimental analyses concerning agricultural study using SAR DATA (1),(2), whereas in Japan, their is no report on that subject. We made images from SAR data, and they were compared with LANDSAT/TM images, Topographical maps and ground truth data.
2.Mthods
2.1.SAR data
Table 1 shows characteristics of SAR instruments and table 2 shows the list of remote sensing data used in this study.
2.2 Analysis instruments
we used the remote sensing analysis system of National Institute of Agro-Environmental sciences. The system has 5EWS, 3 digitizers, a MT unit, 2 types of scanners, a color hard copy machine and a color electrostatic plotter. The system is installed with ERDAS as a image processing data analysis software and ARC/INFO as a geographic information system software.
2.3 Ground truth data
In Hokkaido district, ground truth surveys were made six times as the cooperative works with Hokkaido National Agricultural Experiment station and konsen Agriculture Experiment station. We used topographical maps of 1/25,000 made by Geographical survey of Japan.
Table 1 characteristics of SAR instruments
| Wave length |
incident angle |
polarization |
spatial resolution |
Swath |
| JERS-1 |
L-band
1.275GHz 23.5cm |
38.5 |
HH |
18m looks |
75km |
| ERS-1 |
C-band
5.3 GHz 5.66 |
23 |
VV |
15m looks |
100km |
