Field of View Effect on the Remote Sensing Field Radiometric Measurements
遥感地面辐射观测中的视场效应问题研究

Satellite observations use very narrow field of view(FOV) ( less than 0·01°) but the field measurements use generally very wideFOV(often between 10°and 40°) in order to obtain representative sampling size. This difference may introduce some large errors. The objective of this paper is to propose a practicalmodelingmethod and evaluate field ofview effecton the field reflectancemeasurements for row crops. Themodel considers a row crop as a repetition of rectangularwalls and then translates to a grid mi age with sufficient spatial resolution. The wideFOVreflectance is determined by averaging the reflectance of the elements. Thismodelhas been used for studying a typical row structure crop (maize canopy) for observation angles (from -60°to +60°with step of5°) and for threeFOV(10°, 25°, 45°). The results show thatwide FOVmeasurements generally underestmi ate the reflectance in the red domain (up to -25% of relative reflectancewhen a 25°ofFOV) and have overestmi ation in the near infrared domain (up to 10% of relative reflectancewhen a 25°ofFOV). For different viewing angles, the vegetation contribution is overestmi ated in the illumination direction and underestmi ated in the opposite direction; in the thermal infrared domain, the brightness temperature is generally underestmi ated for viewing angle less than 20°. This study can be used not only to analyze thatFOVeffects, but also tomake optmi al design of observation geometry(FOV, measurement height, measurement spatial size etc. ) for minmi izing the measurement errors, and/or to introduce some corrections to reduce theFOVeffects.