A COMPARISION OF BACKSCATTER COEFFICIENTS OF ALOS PALSAR FBD PRODUCTS IN DIFFERENT GROUND CONDITIONS A.Bormudoi 1 , M.K.Hazarika 1 , R.Schumann 2 , L. Samarakoon 1 1 Geoinformatics Center, Asian Institute of Technology, Klong Luang, Pathumthani, Thailand 12120; Tel: +66-2-524-6148; Fax: +66-2-524-6147 Email:bormudoi@gmail.com 2 RS-Tech Consulting Co., Ltd., Klong Luang, Pathumthani, Thailand 12120; Tel: +66-2-516- 2991; Fax: +66-2-516-4025 Email: roblgs@cscoms.com KEY WORDS: PALSAR, Microwave Backscatter Coefficient ABSTRACT: ALOS PALSAR is a microwave sensor with all weather day and night mapping capability. This makes it extremely useful for mapping ground conditions during cloud cover and night scenarios. The radar equation describes the relationship between the strength of the backscatter signal and the properties of the object. The property is represented by σ˚ (sigma nought). The backscatter coefficient σ˚ varies on both the geometric and dielectric properties of the object and the system parameters of the sensor. Polarization is the orientation of the electric field of the incoming and outgoing signals of the microwave energy emitted from a sensor. The orientation can be either vertical (V) or horizontal (H). This study tried to explore the changes of σ˚ with respect to the two polarization HH and HV for ALOS PALSAR FBD scenes for different landcover types for three conditions on the ground, before, during and a few days after of a flood incident. The study area was parts of the capital city of LaoPDR, Vientiane. It revealed that among all landcover types, paddy and sand were more sensitive to a change of σ˚ and this change was more in the HV polarization. Concrete showed a higher change in HH polarization from pre to flood condition. Bare land showed a higher change in HV from pre to flood condition. For the remaining classes, the changes were less than 1 dB in both the polarizations. 1. INTRODUCTION PALSAR is an L-Band SAR with an active sensor on board. It is capable of beam steering allowing for different swaths. Combined with its flexible geometry, it can operate in a potential 132 modes. Fine beam dual (FBD) mode comes with HH/HV or VV/VH polarization. It has a swath width of 70 Km, off nadir angle of 34.3 degree and an incident angle of (7.5~60) degree. The products have three processing levels namely Raw Data (L 1.0), Single Look complex Products (L 1.1) and Multi look in range and azimuth with ground range geometry and coordinates calculated for each pixel based on ellipsoid GRS80 (L 1.5).The radar equation (Eq. 1) describes the relationship between the strength of the backscattered signal and the properties of the object. The property is represented by σ º ( sigma nought) which is dependent on the geometric and dielectric properties of the object and the system parameters of the sensor.