THE BADAIN JARAN DESERT: REMOTE SENSING INVESTIGATIONS

Approximately half the Badain Jaran Desert in the north-western Alashan Plain of northern China is a sand sea. The remainder is gravel or bedrock. The north-western border of the desert is a playa. The desert has been imaged by both Landsat and the Shuttle Imaging Radar (SIR-A). Landsat analysis indicates there are two dune patterns in the sand sea, north-east oriented crescentic dunes along the northern and western borders, and complex star dunes in the central and eastern desert. Although the orientation and morphology of the dunes are easily visible on Landsat, they cannot be determined with the radar image obtained from the aspect angle used during the SIR-A mission. An abrupt change in wavelength of the dune pattern near the Badain Jaran Playa is mappable on Landsat, but not seen on the radar image. The playa appears to be considerably larger on radar than on the Landsat, and we may be seeing subsurface penetration of dry surficial sands with the radar. Archaeological evidence suggests the playa was the location of prehistoric and historic human activity. SIR-A data indicate the playa was formerly a considerably larger inland lake. THE BADAIN JARAN IS a 44 000 square-kilometre desert in the north-western Alashan Plain ofthe Inner Mongolian Autonomous Region, People's Republic of China. Approximately half the desert is a sand sea. The remainder is bedrock or gobi, loose unsorted gravels predominantly of pebble size (4-64 mm diameter). The Alashan Plain is a broad, tectonically stable platform at an elevation between 1000-2000 metres above sea level. Annual rainfall in the Badain Jaran varies from less than 100 mm in the west to about 250 mm in the east (Zhu and others, 1980). The desert is bounded on the west by the intermittent Ruo Shui stream, and on the south by the Qilian Shan (Qilfan Mountains) and small ranges that separate it from the gobi and sands of the Hexi Corridor. To the north, it merges with black gobi and the plains of the Mongolian People's Republic. The Lang Shan in the east separates the Badain Jaran from the Ulan Buh Desert. The Yabrai Shan separates it from the Tengger Desert to the south. The desert is outlined in Figure 1. There are at least two sand dune patterns in the Badain Jaran Desert. According to Yu and others (1962), lines of crescentic dunes 3-20 metres high, oriented toward the north-east, are distributed along the northern and western borders. These investigators state that the prevailing wind is from the north-west, and the dunes appear to be moving slowly south-eastward. Approximately 5 per cent of these dunes are covered with shrubs. Vegetation cover increases towards two small lakes supplied by the Ruo Shui. Breed (1977) notes that the northern and western boundaries of the main dune field coincide with the 1220 m elevation contour, while the downwind eastern and southern boundaries largely coincide with the 1524 m elevation contour. Dunes averaging 200-300 metres in height, but occasionally more than 500 m high, are in the central and eastern Badain Jaran Desert (Zhu and others, 1980). These dunes may be the tallest sand dunes on Earth. They were mapped by Breed and others (1979) as star dunes with simple crescentic ridges. Although the dunes are very sparsely vegetated, they appear to be stable. The interdunal areas are filled with small dunes, marshes, or salt lakes fed by freshwater springs. The springs are sometimes referred to locally as desert pearls.