COMBINING MULTIFREQUENCY MICROWAVE AND OPTICAL-DATA FOR CROP MANAGEMENT

The potential for he combined use of microwave and optical data for cr op management is explored with the use of images acquired in the visib le, near-infrared, and thermal spectrum and the synthetic aperture rad ar (SAR) wavelengths in the Ku (14.85 GHz) and C (15.3 GHz) bands. The images were obtained during June 1994 and covered an agricultural sit e composed of large fields of partial-cover cotton, near-full-cover al falfa, and bare soil fields of varying roughness. Results showed that the SAR Ku backscatter coefficient (Ku-band sigma degrees) teas sensit ive to soil roughness and insensitive to soil moisture conditions when vegetation was present. When soil roughness conditions were relativel y similar (e.g., for cotton fields of similar row direction and for al l alfalfa fields), Ku-band sigma degrees was sensitive to the fraction of the surface covered by vegetation. Under these conditions, the Ku- band sigma degrees and the optical normalized difference vegetation in dex (NDVI) were generally correlated. The SAR C backscatter coefficien t (C-band sigma degrees) was found to be sensitive to soil moistu re c onditions for cotton fields with green leaf area index (GLAI) less tha n 1.0 and alfalfa fields with GLAI nearly 2.0. For both low-GLAI cotto n and alfalfa, C-band sigma degrees was correlated with measurements o f surface temperature (T-s). A theoretical basis for the relations bet ween Ku-band sigma degrees and NDVI and between C-band sigma degrees a nd T-s was presented and supported with on-site measurements. On the b asis of these findings, some combined optical and radar approaches are suggested for crop management applications. (C) Elsevier Science Inc. , 1997.