| Multiple cropping index is a very important indicator in agricultural statistic in China, which represents the degree of utilizing agriculture resources at time scale and the situation of arable land use effectively. But multiple cropping index is calculated only on the base of statistic data, due to not ensured quality and time, it is urgent to develop a new method extracting multiple cropping index independent of statistic data. So it is a good try to extract multiple cropping index from time series of NDVI. Actually, it is very important and great meaningful for agriculture resources assessment and countrywide food security to monitor multiple cropping index.The rhythm of crop in a year connects the multiple cropping index with time series of NDVI. Extracted from the period of the curve of time series of NDVI, the dynamic information of crop under arable land represents the situation of sequential cropping. With Harmonic ANalysis of Time Series as a core tool, this dissertation reconstructs cloud-free time series of NDVI under the zone of crop phenology, and then calculates the number of peaks using difference methods and develops software. This dissertation extracts multiple cropping index using SPOT/VEGETATION NDVI dataset from the year 1999 to 2002. This dissertation gathered statistic data at different scale, such as county, region, province and countywide. 4 sites with 5 X 5 km2 in typical region have been arranged to collect ground truth data. The dissertation calculates the potential of multiple cropping index by mean of annual accumulated temperature and annual precipitation and the last assesses the potential of multiple cropping index.The main conclusions are as following:(1) The research shows that the curve of time series of NDVI is the records of dynamics of crops cultivated in the arable land, directly presents the physical processes of planting, seeding, heading, ripe, harvest of crop in a year and contains the period rhythm of crop phenology. The information of crop dynamic under arable land extracting from time series of NDVI can represent the performance of sequential cropping. The rhythm of crop in a year connects the time series of NDVI with multiple cropping index and multiple cropping index is equal to the number of peaks of time series of NDVI.(2)The test for extracting multiple cropping index from the year 1999 to 2002 shows the methodology extracting multiple cropping index from time series of NDVI this dissertation proposed are practicable. The results extracted show that multiple cropping index over China fluctuated to contain extent of 150% to 160% from the year 1999 to 2002. Decreasing one season and increasing one season in zone with two crops or three crops per year are main reasons ofmultiple cropping index change in whole country. The use of arable land is comparatively stable in the region of one crop per year and the changes of arable land use are large in the region of two crops per year and three crops per year.(3)Site validation for multiple cropping index show that the accuracy of extracted multiple cropping index is over 96%. Statistical validation shows that there is great consistency between extracted multiple cropping index and statistical data at different scale. So the results of this dissertation are believable.(4)There are positive correlation between maximum of multiple cropping index and annual accumulated temperature above zero and there are also positive correlation between maximum of multiple cropping index and annual precipitation. It is proven that water and thermal condition are main factors that limit the increase of multiple cropping index. There is negative correlation between maximum of multiple cropping index and annual sun duration. It is proven that sun duration is not the factor that limits the increase of multiple cropping index.(5)This dissertation makes model that calculates the potential of multiple cropping index using annual accumulated temperature above zero degree and annual precipitation. The results show that t... |
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