Microwave Remote Sensing for Land cover identification
Sununtha Kingpaiboon
Agricultural Engineering Department, Faculty of Engineering
Khon Kaen University, Khon Kaen 40002 ,Thailand
Tel & Fax 660- 4336-2149;
E-mail: sununtha@kku.ac.th
Abstract
This study considers the potential application of digital JERS-1 SAR data (L- band, 23.5 cm Wavelength),
particularly for land cover monitoring. The SAR data used in this study were acquired on 5 January 1998,
3 April 1998 and 17 May 1998 respectively. These three images available were from the dry season to
the beginning of the rainy season. The study area selected is in the province of Khon Kaen, north-east
Thailand, which is covered by agricultural land, mainly paddy fields and upland crops. Multi - date SAR
data were firstly geocoded to UTM projection, then the data images were scaled from 16 bits to 8 bits.
Some filtering and enhancement methods had to be applied in order to reduce speckle noise and to
contrast the images. Composite color images were produced for visual interpretation and field surveys.
After investigation of the ground truth, representative areas of each land cover type were identified and
allocated to the images. The SAR data of training areas were statistically analysed and were classified
using Maximum Likelihood. The preliminary results showed that general land cover categories could be
well identified, such as water bodies, villages and some lineament features(airfield, road, canal).
Separability matrices indicated the confusion between paddy and upland crops, forest and riparian forest.
Therefore, SAR data are useful for land cover characterization and for hydrological applications,
but a specific methodology for the SAR system needs to be developed.
Introduction
The application of optical data, such as that obtained by LANDSAT and SPOT has a limitation on
weather conditions, particularly for cloud coverage during rainy season. Presently, microwave remote
sensing (radar system) is available and introduces a new generation of remotely sensed data application.
The Synthetic Aperture Radar (SAR), a very high performance, is an active sensor operating in the
microwave region. The advantageous characteristics of SAR are weather and sun-illumination
independence, cloud and rain penetrating capability and fine resolution. The SAR data, on the other
hand, provide substantial information under cloud and haze conditions. These are the major reasons
that the SAR data have become popular in mapping land cover. In addition, the visual appearance of the
SAR image, such as tone, texture, pattern and shape characteristics can be used in visual interpretation.
Microwave is a generic name of electromagnetic spectrum with the wavelength ranging from 1 mm to 1
m. SAR transmits and receives backscattered waves from the ground and land cover (soil, vegetation
etc). An amount of microwave backscattered will differ as a function of topography and geometry of
surface roughness, height and structure of the vegetation, the amount of soil and canopy moisture,
vegetation mass and the differences in the dielectric constant of the objects, therefore, the SAR system
observes in terms of volume information.
Many research applications have been done using SAR data for land cover mapping, particularly in
tropical countries. Land cover classification is also useful for hydrology in terms of the runoff ratio
estimation, the soil moisture and evapotranspiration variation at each land use area. The SAR data have
notable potential to monitor and assess hydrological phenomena, such as the extent of surface water,
inundated area, flood disaster and a real aridity in a river basin. Hydrological applications of remote
sensed data in microwave region have lately attracted attention because of its potential to react to the
extent and amount of water that has remarkably high value of dielectric constant in natural material of the
earth.
The Japanese Earth Resource Satellite (JERS) was used in this preliminary study. JERS-1 was
launched into a sun-synchronous orbit at an altitude of 568 km with a recurrent period of 44 days by the.H- I launch vehicle on February 11, 1992 from the National Space Development Agency of Japan
(NASDA), Tanegashima Space Center. JERS- 1 observes and collects data with Microwave Sensor and
Optical Sensor (OPS). An optical sensor that measures light reflected from the earth’s surface ranging
from visible light to short- wave infrared light. The Synthetic Aperture Radar is an active microwave
sensor. SAR has a ground resolution of 18 m x 18 m and observes for a swathe width of 75 km with
frequency at 1.27 MHz (or 23.5- cm wavelength, L- band radar), HH polariza tion. JERS-1 objectives are
for land surveys, agriculture, forestry, fisheries, environmental and disaster protection and coastal
surveillance.
