Requirement of revisiting period, spatial resolution and spectrum of satellite for grain-soybean rotations monitoring

Abstract: Examination on effect of cereal-soybean rotation is a major business content of agriculture remote sensing monitoring, and the remote sensing data indices are also required for optical satellite development. To meet the requirement on remote sensing monitoring of cereal-soybean rotation, and specially to meet the requirements on the minimal monitoring land parcel, crop types and timeliness, the paper particularly analyzed 3 indices of optical remote sensing satellites: spatial, spectral, and temporal resolutions, and thus provided a theoretical basis for the load design of remote sensing satellites. In setting of spatial resolution, a bulk of arable land was taken as the minimum resolution unit. Based on UAV (unmanned aerial vehicle) images with the resolution of 0.1 m, the paper analyzed the effect of reducing resolution on the visual observation identification capacity on the bulk of arable land by gradually reducing the spatial resolution. In optional spectrum setting, by taking corn and soybean as the major crops of cereal and bean, based on Rapideye images with the spatial resolution of 5 m, and Landsat-OLI images with the spatial resolution of 30 m, the study analyzed the identification capacity on corn and soybean under the combinations of 4 basic wavebands (blue, green, red, and near infrared) and red edge, as well as the combinations of basic wavebands and short wave. In satellite revisiting period setting, the calculation was based on the highest cloud cover frequency of Sichuan Basin of 70%, and the shorter soybean growth period of 90 d. By dividing crop growth stage into 3 periods, i.e. early, middle, and late periods, taking one month as a growth period, the study took 3 clear sky images for each month as the indices to analyze the requirement on the minimum revisiting period of the satellite. The result shows that, to meet the demand of remote sensing examination of crop rotation nationwide, the ideal spatial resolution of remote sensing data shall be better than 0.3 m. By taking spectral setting of basic wavebands (blue, green, red and near infrared) + red edge, or basic wavebands (blue, green, red, and near infrared) + short waveband, the revisiting period has reached 1 time every 3 days. By meeting the above conditions, we can make effective identification on the bulk of arable land with the width of 0.3 m, which is common in China, so as to achieve the target of land identification. It can also achieve the object of identifying the major crop rotation types through effective identification of corns and soybeans in middle growth period by making use of the difference of the spectrum characteristics of red edge and short wave of different crops. High revisiting frequency is used to ensure the acquisition of clear sky images with the 3 periods of acquisition capacity, which not only ensures the acquisition of the images of sensitive periods, but also ensures the acquisition of the image of early periods and later periods. And it can improve the efficiency and accuracy of crop type identification, and thus improve the efficiency of automatic operation on the targets of cereal-bean rotation. The requirement analysis on optical satellite indices in this paper is proposed only for the remote sensing monitoring of cereal-soybean rotation programs. As to whether implement this index or not during the actual design of satellite loads, the satellite load capacity, costs, and the supplement capability of other remote sensing data should be considered, as well as the monitoring demands of other agriculture programs. Proposing a relatively universal satellite design index can lay a foundation for the development of the agriculture remote sensing satellite system.