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Poster Session Q
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A study on the application of aerial Remote Sensing technique to calculate uncultivated coefficient of cropland in Tibet
Liu Jiyuan Yu Zhiqian
Institute of Remote Sensing Application,
Chinese Academy of Science,
Beijing China
Abstract
The remote sensing technique has been used successfully in the surveying and calculation of uncultivated coefficient of cropland in Tibet. The key technical steps include: (1) Taking sampling strip aerial photographs (2) Calculating the value of uncultivated coefficients of sample fields in the infrared colour aerial-photographs by digital image processing systems and other techniques (3) setting up the uncultivated coefficient indexing table in different geomorphologic conditions and types of various cultivated lands, etc. (4) Using infrared colour Air-photo and indexing table together to calculate the uncultivated coefficient of each fields. This method has reduced manpower and expenditure. The study also provided efficient methods to investigate the cultivated areas in other mountainous regiosnand plateaus in China.
Because of limitation of natural condition and affection of cultivating history, vast cultivated lands in the mountainous regions and plateaus in our country are irregular, and mixed with a great quantity of uncultivated components, such as balks interval paths, irrigation channels and small broken pieces of wasteland, etc., There are many problems to survey and calculate cultivated land precisely even using large scale maps and images, therefore, it makes land investigation very difficult. As a result, it is also difficult to estimate agricultural yield without accurate area of cultivated land. In order to find a way to measure cultivated lands by the remote sensing technique, we have applied colour infrared aerial photographs and indexing tables together to determine uncultivated coefficient. This method completely took advantage of remote sensing techniques and image processing systems. In addition, only a small group of investigators was demanded to deal with the critical technical problems, and the final solution was simple and easy to be mastered. Using this method, satisfactory results have been gotten in landuse investigation of whole Tibet.
Taking sample colour infrared aerial photographs and getting indexing tables for uncultivated coefficient calculation
In the method of using remote sensing technique to determine uncultivated coefficient of crops, taking colour infrared aerial photographs and setting up indexing tables are critical steps.
- Data Acquirement and Field Measurement
- Taking colour infrared aerial photographs
To obtain uncultivated coefficients, the infrared colour aerial photographs were taken by way of sampling strip. The strip of sampling flight should cover regions including all types of geomorgraphic condition and cultivated lands, and every types should be repeated a few times. The time we chose was from June to August when the crops are the most flourishing which will make the colour of cultivated lands in photographs most distinct from that of uncultivated ones. The sample strips included every kind of cultivated lands in the east and the south Tibet, with a total length of 1, 698.6km and an area of 15, 798.2 km2
- Spectral reflection measurement and data analysis
The 100 AX multichannel radiometer was used to measure the spectral reflectance's of cultivated and uncultivated lands in Tibet. The data analysis of the spectral reflectance included: (i) calculating the vegetation index of every kind of land, (ii) calculating clustering tendency of spectral reflectance's of every type of land, (iii) estimating the confidence interval of the spectral reflection. The confidence interval was calculated under the hypothesis that the spectral reflectance follows the normal distribution. The value of the confidence interval was worked out by the following formula:
In which m is the average value of the spectral reflectance of one kind of land, d is the standard deviation, n is the sample number, m is equal to 0.05 and t0.05 can be found a t-test table . The results of the confidence interval are shown in Table 1.
Table 1. The distributed area of the spectral reflectance
Of crops and uncultivated fields in Shanan Prefecture of Tibet
TABLE 1 IS MISSING PAGE Q_3_2
It can be seen from the results the results that using the characteristic data of the three-dimension spectral reflection, we are able to effectively distinguish the lands with crops from balks which are bare or sparsely covered with grass, by means of either computer automatic classification of annual discrimination. However, when the balk is completely covered with grass, it is difficult to catch, we have to do manual discrimination on the high-resolution aerial photographs. This result has built a critical foundation of the method to calculate uncultivated coefficients indoors.
- Sampling measurement in the field
In order to determine the accuracy of the uncultivated coefficient gained by indoor methods, we selected a subsample from sample lands. These subsample lands included every type of lands, and each land had been measured in the fields.
Using theodolite and small surveyor's tables, the maps of subsample lands were drawn on the scale of 1:500 or 1:1000. Then, using KP-90 electric planimeter and micro-computer digitizing measurement system, the areas of cultivated lands and whole sampling area were calculated, and finally the uncultivated coefficients were calculated.
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