In order to measure the area of surface warer bodies in Hubei Province

a highly accurate and efficient technique for computer aided recognition of water information using Landsat MSS images was developed. The technique was designed based on the study of spectral signatures of water and non-water information

the data character of ratio images and the enhancement of atmospheric correction.According to the study of spectral signatures

the main information which differentiates water bodies from non-water objects concentrates on band MSS4 and band MSS7. The ratio image of two bands can both merge the information contained -in each band into one image and supperss shadow which is harmul to waiter recognition. Analysis of data character of latio images indicates that the information loss of a ratio image concentrates on the low value section of its value range

when the image is scaled and changed from real type to integer type. Whereas the information in high value section is relatively enhanced by the processing. As the pixels of water bodies possess high values in a MSS4/MSS7 images and low values in MSS7/MSS4 image

the MSS4/MSS7 is superior in water recognition to MSS7/MSS4. But even MSS4/MSS7 images can not completely eliminate dark shadow

the major obstacle to raise the accuracy of water recognition is in mountain areas. This problem is solved by introducing the atmospheric correction to MSS4 before MSS4/MSS7 ratio processing. In a MSS4/MSS7 image with atmospheric correction

the pixel values of water bodies are larger than 1

while the pixel values of dark shadow and other non-water information are less than or equal to 1. Therefore

the water recognition image with high accuracy can be obtained simply by thresholding.The technique is very simple and more precies than common used classification techniques. Its processing speed is more than three times faster than that of mini -distance classification. Besides

the technique can be used not only to MSS images but also to TM images. The successful water area recognition and measurement of whole Hubei Province has shown that the technique can produce perfect results in various areas of different geomorphic types.