This paper attempts to extract urban anisotropic features from two Seasat-1 SAR images with different look directions. Study areas are located in Los Angeles and neighbors of South California, U.S. The sets of data from ascending and descending orbits are used. A city street pattern and other linear feature oriented perpendicular to the radar beam yield very strong radar returns. Therefore, areas which have the oriented feature have different tones on the images obtained during the two orbits. In order to investigate this influence on SAR images, cluster analysis is applied and eight clusters obtained are identified by the aid of city maps and aerial photographs. One cluster includes airports, parks, and golf courses. These areas have no oriented feature. The other clusters correspond to the city street pattern which has the oriented feature. The street pattern oriented within approximately 10°from normal to the look direction is associated with a distinct cluster. The other street pattern oriented above 10°relates to more than one cluster under the influence of urban density.
Multispectral data of the Earth-Atmosphere system obtained from the space-and air-borne sensors provide us with valuable information on environmental situations. However, the apparent radiance distribution at the top differs from its intrinsic distribution of the ground reflectance (the ground albedo), because of the presence of the intervening atmosphere between the sensor and the ground. Such atmospheric effects are caused by the scattering and absorption processes of sunlight by the corresponding constituent particles. The theoretical evaluation of the atmospheric effects on remotely sensed data requires the determination of atmospheric transmittance by various atmospheric particles. We find the results computed from a software program called LOWTRAN 5 are quite useful for such a purpose. It can be said that the LOWTRAN 5 is very important to those having an interest in correcting the remotely sensed data for the atmospheric effects. An aim of the present paper is firstly to give an introduction of the content of the LOWTRAN 5 and secondly to discuss its scope and usefulness, with respect to its application to the LANDSAT MSS data. The LOWTRAN 5 is a software program which calculates the atmospheric transmittance and radiance averaged over 20cm-1 intervals in step of 5cm-1 from 350 to 40, 000cm-1 (0.25 to 28.5μm) and it has been developed at Air Force Geophysics Laboratory in U.S.A.