CALIBRATION OF LARGE FIELD-OF-VIEW THERMAL AND OPTICAL SENSORS FOR PLANT AND SOIL MEASUREMENTS

Infrared thermometers, spectroradiometers, and phototransistor optical sensors have different response characteristics to electromagnetic ra diation, depending upon the position and orientation of the object to be measured within its field-of-view (FOV), its distance from the sens or, and the reflectance or emission characteristics of the object and nearby background. Ideally, thermal or optical sensor response is prop ortional to the amount of exposure of an object within its FOV. Howeve r, the response is also dependent upon the proximity of the object rel ative to the center of the FOV. By relating the composite response of an object within the FOV to the response of its background, an accurat e measurement of the exposure or percent cover of the object can be ma de. Likewise, if the composite and individual component responses with the exception of one are given, the true response of the sensor can b e predicted using a weighted-response function. The correlations betwe en the predicted weighted-response function and the indicated composit e sensor response were high (r2 > 0.9). The weighted-response function can be applied to either temperature, reflectivity, or reflectance FO V.