PORTABLE FOURIER-TRANSFORM INFRARED SPECTRORADIOMETER FOR FIELD-MEASUREMENTS OF RADIANCE AND EMISSIVITY

A hand-held, battery-powered Fourier transform infrared spectroradiome ter weighing 12.5 kg has been developed for the field measurement of s pectral radiance from the Earth's surface and atmosphere in the 3-5-mu m and 8-14-mu m atmospheric windows, with a 6-cm(-1) spectral resolut ion. Other versions of this instrument measure spectral radiance betwe en 0.4 and 20 mu m, using different optical materials and detectors, w ith maximum spectral resolutions of 1 cm(-1). The instrument tested he re has a measured noise-equivalent delta T of 0.01 degrees C, and it m easures surface emissivities, in the field, with an accuracy of 0.02 o r better in the 8-14-mu m window (depending on atmospheric conditions) , and within 0.04 in accessible regions of the 3-5-mu m window. The un ique, patented design of the interferometer has permitted operation in weather ranging from 0 to 45 degrees C and 0 to 100% relative humidit y, and in vibration-intensive environments such as moving helicopters. The instrument has made field measurements of radiance and emissivity for 3 yr without loss of optical alignment. We describe the design of the instrument and discuss methods used to calibrate spectral radianc e and calculate spectral emissivity from radiance measurements. Exampl es of emissivity spectra are shown for both the 3-5-mu m and 8-14-mu m atmospheric windows.