C-band Radar Imagery Research Articles

Applying polarimetric radar imagery for mapping the productivity of wheat crops

Airborne, fully polarimetric C-band radar imagery was acquired over an agricultural test site located in southern Ontario (Canada) on 30 June 1999. Approximately 2 weeks after this image acquisition, yield-monitor data were collected over two wheat fields. Zones of higher productivity had higher radar backscatter, for linear (HH, VV, HV) and circular (RR, LR) polarizations. Zones of productivity were classified using backscatter from the linear polarizations, and these classified maps agreed well with the maps generated by the yield monitors. The linear cross-polarization (HV) provided the greatest contrast between zones of high and low productivity, although the height of the cross-polarization pedestal also varied between these two classes. No significant differences were observed between high- and low-producing zones using either the copolarization pedestal height or the copolarization phase difference. This study demonstrated that polarimetric radar parameters such as the linear and circular polarizations and the cross-polarization pedestal height are sensitive to differences in wheat productivity.

Detecting seasonal flooding cycles in marshes of the Yucatan Peninsula with SIR-C polarimetric radar imagery

Polarimetric L- and C-band radar imagery from the shuttle imaging radar-C (SIR-C) were acquired over wetlands of the Yucatan Peninsula during the dry (April) and wet (October) seasons of 1994. Field surveys during the flights recorded biophysical data and water depth in 11 marsh sites containing communities of three principal emergent macrophytes: Cladium jamaicense, Typha domingensis, and Eleocharis cellulosa. The only major seasonal change was in flooding. Seasonal changes in polarimetric backscatter magnitude (HH, VV, and CS=(HV+VH)/2) and phase [βH-V phase differenceβ=PD) were extracted for a stable evergreen mangrove forest calibration site, which confirmed that the absolute calibration of the Yucatan imagery exceeded the SIR-C system calibration. We estimate that seasonal changes of ⩾2dB in backscatter magnitude and ⩾10° in phase (PD) are significant in our data. Seasonal changes in L- and C-band magnitude and phase were extracted from the 11 marshes, and significant changes above the calibration limit were noted. Increased flooding in the marshes was detected by: 1) an increase in backscatter magnitude in marshes with tall, dense cover; 2) a decrease in backscatter magnitude in marshes with short, sparse cover, and 3) an increase in PD in all types of marshes. Magnitude increases result from an increase in double-bounce interactions between the emergent vegetation and water surface, whereas decreases result from an increase in forward scattering off the open water. Average PD values increase owing to an absolute or relative increase in double- compared with single-bounce interaction. Changes from dry or partially flooded to completely flooded, as well as increases in water depth, could be detected by most of the polarimetric parameters, but changes from dry to partially flooded could not. C-band PD (CPD) was the radar parameter most sensitive to flooding. CPD changed significantly for all eleven marshes, followed by L-band PD (LPD) and LVV (nine marshes) and LHH, LCS, and CVV (seven marshes). CHH detected significant changes in five marshes but produced changes of ±1.8–1.9 dB (just below our estimated calibration limit) in four others. An evaluation of current spaceborne radars indicates that a combination of the European Remote Sensing Satellite (ERS-1,2) and Radarsat radars could detect seasonal flooding in a wide variety of marsh ecosystems, excluding partial flooding and flooding in small patches of short, sparse vegetation.