Hot spot measurements at high angular resolution using POLDER data over Australia

The hot spot is an enhancement in the optical reflectance of land surfaces at view directions close to the antisolar (exact backscatter) direction. The two-dimensional imaging capability of POLDER on ADEOS has previously been exploited to measure the hot spot on homogeneous land surfaces from space with an angular resolution of 0.3degrees, by using the variation in view direction with spatial position across a single image frame. This paper extends that approach to inhomogeneous areas by estimating the non-hot-spot component of the reflectance from views of the scene at directions far from the hot spot direction. The technique is robust enough to be applied to essentially any POLDER image in which the hot spot falls on cloud-free land. On a single orbit down eastern Australia, the half-width of the hot spot at 670 nm has the rather restricted range of 1degrees-2degrees, despite sampling a broad range of land cover types.