ABSTRACT
Airborne radiometers have been employed for various remote sensing applications, including optical characterizations of forest canopies [1], surface reflectance factor retrievals from satellite imagery [2], spatial extrapolation of evaporation over agricultural fields [3], and scaling up and validation of satellite data products [4,5]. These studies have found the utility of airborne radiometers because (1) they can rapidly obtain data over rather large areas, encompassing fields having considerably different surface properties [3]; and (2) they can measure reflectance factors of tall objects that cannot be reached from ground (e.g., forest canopies) [1]. Airborne or helicopter-based radiometers are typically flown at low altitudes (<150 m above ground level) “below atmosphere.” On the ground, another radiometer (the same model) cross-calibrated with the ones in air is set up, continuously measuring radiances reflected off a white reference panel during the flights, to later convert airborne data to reflectance factors by ratioing (e.g., Holm et al. [5]).
