Optimizing the observation time for bare arable land to determine mean diurnal albedo in relation to roughness

Abstract

ABSTRACT It is assumed that the approximation of the albedo values of the Earth’s surface components using satellite data obtained at the optimal time (T o) when these areas’ albedo reach mean diurnal values (α d), rather than these instantaneous values, allows Earth’s overall climate change to be modelled with greater accuracy. The T o values were investigated using examples of arable land areas in the 33 most extensive agricultural regions of the world, on given days of the year when the largest sections of these land areas become bare after major crops were planted under conventional tillage. This study is based on processed data obtained from nearly 900 soil reflectance spectra, representing 24 major soil groupings on 6 continents, assuming that these soils, which were either shaped by a plough (Pd) or smoothing harrow (Hs), were air-dried. It was found that in the morning the T o, expressed in solar local time, was expected to be earlier for rough bare soil surfaces than smooth ones. In the afternoon this relationship was reversed. The differences in the T o values that resulted from the different surface roughness of the same soils (formed by Pd and Hs) were 5–10 minutes. Deviations of about 5–20 minutes from T o in the observations of the studied land areas generated errors of ±2% in the approximations of their α d values.