Radar Backscattering Measurements of Paddy Rice Field using Multifrequency(L, C and X) and full Polarization Yi-hyun Kim 1 , Suk-young Hong 1 and Hoonyol Lee 2 1 National Institute of Agricultural Science and Technology(NIAST), RDA, Suwon 441-707, Korea 2 Department of Geophysics, Kangwon National University, Chuncheon 200-701, Korea yhkim75@rda.go.kr, syhong@rda.go.kr, hoonyol@kangwon.ac.kr Abstract-The objective of this study is to measure backscattering coefficients of paddy rice using L, C, X-bands scatterometer system during a rice growth period and relationship between backscattering coefficients and rice growth variables with full polarization and various angles. The measurement was conducted at an experimental field located in National Institute of Agricultural Science and Technology (NIAST), Suwon, Korea. The rice cultivar was a kind of Japonica type, called chuchung. The scatterometer system consists of dual-polarimetric square horn antennas, HP8720D vector network analyzer (20MHz ~ 20GHz), RF cables, and a personal computer that controls frequency, polarization and data storage. The backscattering coefficients were calculated by applying radar equation for the measured at incidence angles between 20° and 60° for four polarization (HH, VV, HV, VH), respectively, and compared with rice growth data such as plant height, stem number, biomass, dry weight and LAI that were collected at time of each scatterometer measurement simultaneously. Keyworlds—Backscattering coefficients; Scatterometer system; network analyzer; polarization; rice growth data 1. INTRODUCTION Rice is one of the major crops in Korea. In spite of its importance as a food source, there have been few attempts to monitor rice growth and study backscattering characteristics with a microwave instrument from space- ground platform. Microwave radar can penetrate cloud cover regardless of weather conditions and it can be used day and night. Especially a ground-based polarimetric scatterometer has advantage of monitoring crop conditions continuously using full polarization and various frequencies. Many plant parameters such as leaf area index (LAI), biomass, plant height are highly correlated with backscattering coefficients and according to frequency, polarization between plant parameters and backscattering coefficients was different (Ulaby, 1984; Bouman, 1991). Le Toan et al. (1997) showed the potential SAR backscatter data for rice crop monitoring based on both satellite and ground based scatterometer measurements. Hong et al. (2000) analyzed RADARSAT data (5.3 GHz, hh- polarization, and incidence angles between 36° and 46°) for monitoring the rice growth in Korea. In this study, we examine the temporal behaviour of the radar backscatter from rice crops during the growth period at multi-frequency (L, C, X-band) with angular response. 2. MATERIAL AND METHOD The test site was located in NIAST experimental field (37° 15’ 28.0” N, 126° 59’ 21.5” E) Suwon, Korea. The rice cultivar was a kind of Japonica type, called chuchung. The size field was about 660m 2 . Table 1 show the scatterometer system specification. Table 1. Specification of the scatterometer system Specification L-Band C-Band X-Band Center Frequency 1.27 GHz 5.3 GHz 9.65 GHz Bandwidth 0.12 GHz 0.6 GHz 1 GHz Number of Frequency Points 201 801 1601 Antenna Type Dual polarimetric horn Dual polarimetric horn Dual polarimetric horn Antenna Gain 12.4dB 20.1dB 22.4dB Polarization HH, VV, HV, VV HH, VV, HV, VV HH, VV, HV, VV Incident Angle 20° ~ 60° 20° ~ 60° 20° ~ 60° Platform Height 4.16m 4.16m 4.16m The system mainly composed of dual-polarimetric square horn antennas, vector network analyzer (VNA), RF cables, and a personal computer. The VNA-based polarimetric scatterometer operates in a stepped-frequency sweep mode.