Estimation of Wheat Development Periods on a Grid Scale upon Potential Temperature

Wheat development period (WDP) data of different scales on grids are necessary in monitoring by remote sensing and quantitative assessment during late freezing. Taking Henan Province as an example, the calculation of WDP on grids is proposed upon potential temperature by GIS considering the elevation of different grids, which is a strong mechanism. At first, it is divided into five different ecological regions according to different climatic types, which is Ⅰ area (the north of Henan) , Ⅱ area (the west of Henan) , Ⅲ area (the middle of Henan) , Ⅳ area (the plain in eastern Henan) and Ⅴarea (the south of Henan) , respectively. The equation of accumulated temperature (E-AT) between turning green and jointing is constructed based on more than two decades WDP records. To consider the effect of elevation upon interpolation, equations of potential temperature and stateas well as ARCGIS software are used to calculate grid potential temperature; to reckon air pressure etc. on grids; to deduce grid temperature data based on the above results; to perform winter wheat elongation stage on grids which are matched with remote sensing data according to E-AT at last. The results show that the method to calculate WDP indirectly has much new idea and strong mechanism; the way to perform data of wheat turning green in grids by means of meteorological index is more theoretical and accurate than that of setting the same date of WDP in the same climatic region during the calculation of WDP; the error resulting from this method is two days or so, and is within the permitted error which is about 5 days during monitoring wheat late freezing; the error by the indirect way to calculate WDP after obtaining potential temperature and air pressure is lowercompared with results from directly interpolating temperature and other ways considering terrain height. And the result can be used during monitoring late frost by remote sensing.