Korean Journal of Remote Sensing, Vol.25, No.1, 2009, pp.31~44 Estimation of Paddy Rice Growth Parameters Using L, C, X-bands Polarimetric Scatterometer Yi-Hyun Kim*, Suk-Young Hong*, and Hoonyol Lee** *National Academy of Agricultural Science, Rural Development Administration **Department of Geophysics, Kangwon National University Abstract : The objective of this study was to measure backscattering coefficients of paddy rice using a L-, C-, and X-band scatterometer system with full polarization and various angles during the rice growth period and to relate backscattering coefficients to rice growth parameters. Radar backscattering measurements of paddy rice field using multifrequency (L, C, and X) and full polarization were conducted at an experimental field located in National Academy of Agricultural Science (NAAS), Suwon, Korea. The scatterometer system consists of dual-polarimetric square horn antennas, HP8720D vector network analyzer (20 MHz ~ 20 GHz), 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 with 5 interval for four polarization (HH, VV, HV, VH), respectively. We measured the temporal variations of backscattering coefficients of the rice crop at L-, C-, X-band during a rice growth period. In three bands, VV-polarized backscattering coefficients were higher than hh-polarized backscattering coefficients during rooting stage (mid-june) and HH-polarized backscattering coefficients were higher than VV-, HV/VH-polarized backscattering coefficients after panicle initiation stage (mid-july). Cross polarized backscattering coefficients in X-band increased towards the heading stage (mid-aug) and thereafter saturated, again increased near the harvesting season. Backscattering coefficients of range at X-band were lower than that of L-, C-band. HH-, VV-polarized s steadily increased toward panicle initiation stage and thereafter decreased, and again increased near the harvesting season. We plotted the relationship between backscattering coefficients with L-, C-, X-band and rice growth parameters. Biomass was correlated with L-band hh-polarization at a large incident angle. LAI (Leaf Area Index) was highly correlated with C-band HH- and cross-polarizations. Grain weight was correlated with backscattering coefficients of X-band VV-polarization at a large incidence angle. X-band was sensitive to grain maturity during the post heading stage. Key Words : Backscattering coefficients, Full polarization, L-band, C-band, X-band, Rice growth, Biomass, LAI. hoonyol@kangwon.ac.kr 31
Korean Journal of Remote Sensing, Vol.25, No.1, 2009 s 32
Estimation of Paddy Rice Growth Parameters Using L, C, X-bands Polarimetric Scatterometer Fig. 1. Consist of polarimetric scatterometer system. 33
Korean Journal of Remote Sensing, Vol.25, No.1, 2009 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 12.4 db 20.1 db 22.4 db Polarization HH, VV, HV, VH HH, VV, HV, VH HH, VV, HV, VH Incident angle 20 ~ 60 20 ~ 60 20 ~ 60 Platform height 4.16 m 4.16 m 4.16 m P r P t G t G r l 2 P r = s (1) (4p) 3 R 4 P t G t G r l s R s A s 0 s = (2) A Z i = a i e jfi (3) 34
Estimation of Paddy Rice Growth Parameters Using L, C, X-bands Polarimetric Scatterometer a f 8 1 Z = S (a i cosf i + ja i sinf i ) (4) 8 i=1 U P t P r 2 U 2 V = ( r ) V t = (5) s P 10 log( ) [ ] = 20 log U = 10 log G t G r l 2 r s (6) P (4p) 3 R 4 t \s(db) = 10 log s = 20 log U _ G t (db) _ G r (db) _ 20 log l + 30 log 4p + 40 log R G t G r A DR A = l (7) cosq i DR DR = c/2b q i l R q R q L _ band : s (db) = 20logU+21.35(dB)+30logR+10log cosq i C _ band : s (db) = 20logU+30.27(dB)+30logR+10log cosq i X _ band : s (db) = 20logU+32.21(dB)+30logR+10log cosq i P r P t 35
Korean Journal of Remote Sensing, Vol.25, No.1, 2009 (a) Incident angle : 30 (b) Incident angle : 40 (c) Incident angle : 50 (d) Incident angle : 60 Fig. 2. Temporal variations of backscattering coefficients at polarization and incident angle 30 ~ 60 for the L-band. (a) Incident angle : 30 (b) Incident angle : 40 (c) Incident angle : 50 (d) Incident angle : 60 Fig. 3. Temporal variations of backscattering coefficients at polarization and incident angle 30 ~ 60 for the C-band. 36
Estimation of Paddy Rice Growth Parameters Using L, C, X-bands Polarimetric Scatterometer (a) Incident angle : 30 (b) Incident angle : 40 (c) Incident angle : 50 (d) Incident angle : 60 Fig. 4. Temporal variations of backscattering coefficients at polarization and incident angle 30 ~ 60 for the X-band. Fig. 5. Temporal variation in rice plant height. Fig. 6. Temporal variation in rice Leaf Area Index. 37
Korean Journal of Remote Sensing, Vol.25, No.1, 2009 Fig. 7. Temporal variation in rice fresh weight. Fig. 8. Temporal variation in rice grain dry weight. Table 2. Correlation coefficients between backscattering coefficients and rice growth parameters at L-band VV HH VV HV HH HV Incident Plant LAI Tfw Tdw Plant LAI Tfw Tdw Plant LAI Tfw Tdw Incident angle height LAI (g/m Tfw 2 ) (g/m Tdw 2 ) (g/m Tfw 2 ) (g/m Tdw 2 ) (g/m Tfw 2 ) (g/m Tdw 2 ) angle (g/m 2 ) (g/m 2 height LAI ) (g/m 2 ) (g/m 2 height LAI (cm) (cm) ) (cm) (g/m 2 ) (g/m 2 ) 20-0.93*** -0.81** -0.90*** -0.87*** -0.56* -0.20 ns -0.37 ns -0.32 ns 0.21 ns 0.38 ns 0.29 ns 0.32 ns 25-0.53* -0.20 ns -0.37 ns -0.32 ns 0.24 ns 0.44* 0.38 ns 0.38 ns 0.76** 0.85** 0.81** 0.81** 30-0.01 ns 0.28 ns 0.15 ns 0.18 ns -0.39 ns -0.38 ns -0.42* -0.40 ns 0.91*** 0.77** 0.85** 0.82** 35-0.49* -0.63* -0.58* -0.62* 0.40 ns 0.25 ns 0.31 ns 0.28 ns 0.89*** 0.71** 0.80** 0.78** 40 0.81** 0.58* 0.70* 0.68* 0.74** 0.73** 0.76** 0.72** 0.89*** 0.81** 0.86*** 0.85** 45 0.92*** 0.78** 0.87*** 0.85** 0.94*** 0.89*** 0.92*** 0.91*** 0.90*** 0.91*** 0.90*** 0.86*** 50 0.87*** 0.63* 0.75** 0.73** 0.94*** 0.91*** 0.97*** 0.98*** 0.92*** 0.86*** 0.90*** 0.89*** 55 0.85** 0.62* 0.75** 0.73** 0.93*** 0.90*** 0.93*** 0.91*** 0.90*** 0.88*** 0.92*** 0.92*** 60 0.87*** 0.74** 0.81** 0.79** 0.86*** 0.88*** 0.89*** 0.87*** 0.84** 0.90*** 0.91*** 0.91*** Tfw : Total fresh weight, Tdw : Total dry weight ns : Non significance * : level of significance p<0.05 ** : level of significance p<0.01 *** : level of significance p<0.001 38
Estimation of Paddy Rice Growth Parameters Using L, C, X-bands Polarimetric Scatterometer Table 3. Correlation coefficients between backscattering coefficients and rice growth parameters at C-band VV HH VV HV HH HV Incident Plant LAI Tfw Tdw Plant LAI Tfw Tdw Plant LAI Tfw Tdw Incident angle height LAI (g/m Tfw 2 ) (g/m Tdw 2 ) (g/m Tfw 2 ) (g/m Tdw 2 ) (g/m Tfw 2 ) (g/m Tdw 2 ) angle (g/m 2 ) (g/m 2 height LAI ) (g/m 2 ) (g/m 2 height LAI (cm) (cm) ) (cm) (g/m 2 ) (g/m 2 ) 20-0.94*** -0.74** -0.84** -0.83** -0.84** -0.67* -0.76** -0.75** 0.81** 0.67* 0.74** 0.71** 25 0.74** 0.72** 0.75** 0.74** 0.48* 0.48* 0.46* 0.48* 0.85** 0.92*** 0.90*** 0.90*** 30 0.82** 0.78** 0.82** 0.81** 0.86*** 0.83** 0.84** 0.85** 0.83** 0.92*** 0.91*** 0.92*** 35 0.67* 0.70* 0.67* 0.68* 0.93*** 0.84** 0.90*** 0.89*** 0.88*** 0.91*** 0.89*** 0.88*** 40 0.38 ns 0.55* 0.50* 0.50* 0.95*** 0.87*** 0.92*** 0.91*** 0.91*** 0.92*** 0.88*** 0.87*** 45 0.38 ns 0.64* 0.56* 0.58* 0.90*** 0.91*** 0.93*** 0.93*** 0.95*** 0.88*** 0.90*** 0.87*** 50 0.64* 0.76** 0.74** 0.73** 0.94*** 0.95*** 0.93*** 0.93*** 0.90*** 0.85** 0.88*** 0.87*** 55 0.56* 0.70* 0.68* 0.67* 0.93*** 0.90*** 0.92*** 0.92*** 0.88*** 0.83** 0.86*** 0.84** 60 0.38 ns 0.46* 0.44* 0.43* 0.92*** 0.92*** 0.91*** 0.92*** 0.91*** 0.83** 0.88*** 0.86*** * Tfw : Total fresh weight, Tdw : Total dry weight ns : Non significance * : level of significance p<0.05 ** : level of significance p<0.01 *** : level of significance p<0.001 Table 4. Correlation coefficients between backscattering coefficients and rice growth parameters at X-band VV HH VV HV HH HV Incident Plant LAI Tfw Tdw Plant LAI Tfw Tdw Plant LAI Tfw Tdw Incident angle height LAI (g/m Tfw 2 ) (g/m Tdw 2 ) (g/m Tfw 2 ) (g/m Tdw 2 ) (g/m Tfw 2 ) (g/m Tdw 2 ) angle (g/m 2 ) (g/m 2 height LAI ) (g/m 2 ) (g/m 2 height LAI (cm) (cm) ) (cm) (g/m 2 ) (g/m 2 ) 20 0.26 ns 0.41* 0.32 ns 0.32 ns 0.68* 0.63* 0.64* 0.63* 0.80** 0.83** 0.82** 0.82** 25 0.62* 0.70* 0.68* 0.67* 0.72** 0.66* 0.68* 0.67* 0.73** 0.74** 0.74** 0.72** 30 0.46* 0.57* 0.54* 0.52* 0.82** 0.82** 0.84** 0.82** 0.65* 0.75** 0.70** 0.69** 35 0.50* 0.67* 0.62* 0.61* 0.81** 0.83** 0.80** 0.83** 0.71** 0.79** 0.74** 0.74** 40 0.43* 0.61* 0.55* 0.56* 0.72** 0.83** 0.79** 0.81** 0.67* 0.81** 0.74** 0.74** 45 0.33 ns 0.45* 0.42* 0.40* 0.74** 0.80** 0.81** 0.82** 0.76** 0.81** 0.81** 0.79** 50 0.23 ns 0.29 ns 0.28 ns 0.24 ns 0.71** 0.77** 0.75** 0.76** 0.74** 0.74** 0.76** 0.73** 55-0.10 ns -0.20 ns -0.13 ns -0.18 ns 0.75** 0.81** 0.80** 0.80** 0.82** 0.79** 0.83** 0.81** 60-0.25 ns -0.44* -0.36 ns -0.41* 0.75** 0.79** 0.79** 0.78** 0.81** 0.71** 0.77** 0.75** * Tfw : Total fresh weight, Tdw : Total dry weight ns : Non significance * : level of significance p<0.05 ** : level of significance p<0.01 *** : level of significance p<0.001 39
Korean Journal of Remote Sensing, Vol.25, No.1, 2009 Table 5. Correlation coefficients between L-, C-, X-band backscattering coefficients and grain dry weight L-band C-band X-band L-band C-band X-band Incident angle VV HH HV VV VV HH HH HV HV VV VV HH HHHV HV 20-0.96*** -0.85** -0.64* -0.50* -0.19 ns 0.26 ns -0.54* -0.05 ns 0.10 ns 25-0.97*** -0.74** 0.06 ns -0.19 ns -0.39 ns -0.70* -0.33 ns 0.35 ns 0.56* 30-0.78** -0.64* 0.53* -0.55* -0.38 ns -0.55* 0.51* 0.31 ns -0.45* 35 0.43* 0.72* 0.72* -0.81** -0.32 ns 0.27 ns 0.70* -0.30 ns -0.40* 40 0.61* 0.40* 0.66* -0.22 ns -0.80** -0.32 ns 0.78** -0.36 ns -0.45* 45 0.75** 0.23 ns 0.63* -0.39 ns -0.78** -0.13 ns 0.87*** 0.39 ns 0.58* 50 0.71* -0.67* 0.29 ns -0.16 ns -0.52* 0.23 ns 0.83** 0.55* 0.65* 55 0.58* -0.29 ns 0.07 ns 0.17 ns -0.77** 0.43* 0.80** 0.70* 0.71* 60 0.30 ns 0.18 ns -0.10 ns 0.67* -0.70* 0.51* 0.81** 0.74** 0.69* ns : Non significance * : level of significance p<0.05 ** : level of significance p<0.01 *** : level of significance p<0.001 Table 6. Optimum condition between backscattering coefficients at and rice growth parameters Band Polarization Incident angle Correlation coefficient (r) Plant height(cm) C-band HV 45 r=0.95*** LAI C-band HH 50 r=0.95*** Biomass(g/m 2 ) L-band HH 50 r=0.96*** Grain dry weight(g/m 2 ) X-band VV 45 r=0.87** ** : level of significance p<0.01 *** : level of significance p<0.001 y=0.01790x 2 +16.7038x+406.4284 R 2 =0.92*** (n=20) R 2 =0.92*** RMSE=3.17884 (a) (b) Fig. 9. (a) Relationship between backscattering coefficient in C-band(VH, 45 ) and plant height during rice growth stage. (b) Relationship between Measured and estimated plant height during rice growth stage. 40
Estimation of Paddy Rice Growth Parameters Using L, C, X-bands Polarimetric Scatterometer y=0.0035x 2 +0.3633x+8.4322 R 2 =0.92*** (n=20) R 2 =0.91*** RMSE=0.46917 (a) (b) Fig. 10. (a) Relationship between backscattering coefficient in C-band(HH, 50 ) and LAI during rice growth stage. (b) Relationship between Measured and estimated LAI during rice growth stage. y=0.5475x 2 +44.6724x+893.1666 R 2 =0.95*** (n=19) R 2 =0.94*** RMSE=5.75061 (a) (b) Fig. 11. (a) Relationship between backscattering coefficient in L-band(HH, 50 ) and fresh weight during rice growth stage. (b) Relationship between Measured and estimated fresh weight during rice growth stage. 41
Korean Journal of Remote Sensing, Vol.25, No.1, 2009 y=-0.0402x 2-1.5940x+9.0138 R 2 =0.82** (n=8) R 2 =0.82*** RMSE=1.37052 (a) Fig. 12. (a) Relationship between backscattering coefficient in X-band(VV, 45 ) and grain dry weight during rice growth stage. (b) Relationship between Measured and estimated grain dry weight during rice growth stage. (b) 42
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