1. INTRODUCTION
Penetration is an important characteristic for SAR. Over the last two decades, many aircraft and spaceborne images including Seasat L-band (1.30 GHz, 23 cm) and Shuttle Imaging Radar L-band (1.30 GHz, 23 cm and 1.25 GHz, 24 cm), C-band (5.0 GHz, 6cm) and X-band (10.0 GHz, 3cm) images have been acquired of sand covered desert areas, principally in Africa and North America. It was famous that investigators found the ancient drainage patterns (paleodrainage valleys or “radar-rivers”) eroded into the bedrock as well as faults and terraces that underlie the sand sheet in Eastern Sahara based on Shuttle Imaging Radar (SIR-A) images [1]. The past researches mostly focus on where the penetration effect happened, and the qualitative, theoretical analysis. Although the penetration capability for SAR is understood, a quantitative, exact formula or model to describe the behavior has not been generated.