This paper is concerned with a new detection method of snow covered area in LANDSAT imagery. For the purpose, A degaard's method has been well-known, in which if brightness of a pixel is greater than a threshold value, its domain is classified as snow covered. The threshold value is specified as a separating value between the brightness distributions of snow covered and snow free areas. The method, however, is not necessarily effective in mountainous areas because snows in shady areas or in sunny areas but not directed to the sun are not so bright. In the new method, by refering to a digital elevation model and the sun position at image collection, domains of each pixel are classified into three categories, i.e., (1). sunny domain directed to the sun, (2). sunny domain but undirected to the sun, (3).completely shady domain. By applying three threshold values adaptively due to domain categories, snow covered areas can be detected by following to φ degaard's method. Results of detection for LANDSAT-MSS data of various seasons, the new method efficiently detect snow covered area, especially for the data when the elevation is low.
Some features of drift ice in the Liaodong Wan (bay) are described by using the Landsat images. Drift ice is able to see every year for four winter seasons in this bay since 1982. The extent and state or stage of sea ice, numbers and sizes of floe are seen on the images. The changes of forms of drift ice and ice fields are observed by comparing sequential images. They say the southern limit of the drift ice is 44° N at the southern part of the Okhotsk Sea in the northern hemisphere. However it is not 44°N but 38' 30'N or more southern part in the Liaodong Wan and Bohai. Sea ice is seen till 37°10' in the Bohai. The reason why the ports of Dalian and Lushun do not freeze is also mentioned.
Making use of a breadboard model of Microwave Scanning Radiometer (MSR) of Marine Observation Satellite (MOS)-1 and other instruments, field ex-periments to obtain physical properties of snow and radiometric characteristics were made for 3 consecutive winter seasons from 1982 to-1984. Analyses of the data indicate the decrease of microwave brightness temperature (Tb) with increasing snow depth, however beyond the depth of the minimum Tb a reverse tendency, i.e. increase of Tb with increasing snow depth, is recognized in some cases although the value itself is small. It is proposed to call the phenomenon a brightening effect. It is found that an emission model of 3rd order polynomials in terms of parameters which are combinations of optical depth and albedo can satisfactorily explain the phenomenon.
A new technique has been studied to make clearer water-land boundary on the thermal imagery. In this technique, near infrared information is converted to one bit flag which separates water and land parts, and it is combined with seven bits thermal infrared information to make eight bits composite data. The technique was applied to some Landsat TM image data. The result shows that the reasonable separation is realized between water and land, and that the thermal information in each of the parts can be enhanced in level 0-127 for water and 128-255 for land, respectively. All of image processing processes was programed by FORTRAN 77 on the basis of a personal computer.
Effects of wind-generated roughness on the sea surface microwave emission at 6.7 and 18.6GHz are discussed in vertical and horizontal polarizations in angular range of incidence from 20f to 70 degrees, based on observed data. The sea surface brightness temperature (microwave temperature), employed for discussions on microwave emissivity, depends on the sea surface roughness generated by wind and developed with increasing wind speed. Then wind speed is adopted instead of the sea surface roughness. It is another reason for adopting wind speed that Cox and Munk have alredy reported that the rms slope of the sea surface is closely correlated with wind speed. Such wind speed sensitivity of microwave emission also depends on observational conditions such as frequency, incidence angle and polarization. The vertically polarized sea surface brightness temperature is insensitive to wind speed in the region of 53 degrees of incidence angle at both frequencies, however, this temperature increases below and decreases above this angle with increasing wind speed and larger wind-induced changes in brightness temperature are observed at lower and higher incidence angles at both frequencies. The horizontally polarized temperature is less dependent on incidence angle at both frequencies, but is more sensitive to wind speed than the vertically polarized one over the entire range of incidence angle except the regions of 20 and 70 degrees at both frequencies. Finally our results are compared with those already reported at several frequencies by many investigators. Wind speed sensitivities are rather different, but quite the same emissive characteristics are observed.
The functions of Beijing Remote Sensing Satellite Ground Station are receiving, processing, archiving and distribution of Landsat and other remote sensing satellite data. The station can cover approximately 80% of land territory of China. It is planned a second remote sensing ground-station which will be built in Urumchi in the westen China. These two stations will then cover whole land territory of China. A third station in southern part of China is also under planning stage. It can, together with Beijing ground station, acquire data over the sea around China and remote islands, as well. Present receiving station is built approximately 100km to the north of Beijing. The receiving system with 10mφ AZ-EL antenna has capability of receiving both S-and X-band data of Landsat and SPOT. SPOT receiving system has not been completed yet. Received data are recoverd on HDDT and transferred to Beijing center for processing. Data distribution is handled at Beijing center.