RapidEye卫星红边波段对农作物面积提取精度的影响

    Impact of red-edge waveband of RapidEye satellite on estimation accuracy of crop planting area

    • 摘要: 在传统的可见光与红外波段基础上增加红边波段(690~730 nm),是当前高分辨卫星传感器研制的明显趋势。德国RapidEye卫星携带有红边波段传感器,该文基于黑龙江省北安市东胜乡2014年7月27日的RapidEye遥感数据,采用监督分类的方法,通过计算有红边参与条件下、无红边参与条件下,玉米、大豆及其他3种地物类型的可分性测度、分类精度及景观破碎度等指标,比较分析了2种波段组合方式下的红边波段对农作物面积提取精度的影响。其中,监督分类的训练样本是以覆盖研究区的2 km×2 km格网为基本单元,在玉米和大豆面积比例等概率原则下,选取了10个网格作为训练样本,样方内作物的识别采用目视解译的方式完成。精度验证是采用覆盖研究区的农作物面积本底调查结果评价的,本底调查数据是在5 m空间分辨率Rapideye数据初步分类基础上,根据多时相Landsat-8/OLI(Operational Land Imager)数据季节变化规律,结合地面调查,采用目视修正的方法完成。结果表明,有红边参与的玉米、大豆和其他3种地物类型识别的总体精度为88.4%,Kappa系数为0.81,玉米、大豆和其他3种地物类型的制图精度分别为93.1%,86.0%和87.3%;没有红边参与的3种地物识别的总体精度为81.7%,Kappa系数为0.71,玉米、大豆和其他3种地区类型的制图精度分别为83.9%,73.4%和84.6%;通过引入红边波段,3种地物的总体识别精度提高了6.7百分点,玉米、大豆和其他3种地物类型的识别精度分别提高了9.2百分点,12.6百分点和2.7百分点。利用Jeffries-Matusita方法计算了3种地物的可分性测度,玉米-大豆、玉米-其他、大豆-其他的可分性测度分别由0.84变为1.73、1.37变为1.81、1.27变为1.29;采用破碎度指数计算了景观破碎度,地块数量减少了69.2%,平均地块面积增加了2.2倍,平均地块周长增加了60.50%,地块面积与周长比增加了1.0倍。由上述研究结果可以看出,通过红边波段的引入,增加了地物的间的可分性测度,减少了“椒盐”效应造成的景观破碎度的增加,农作物面积识别整体精度得到了提高。目前搭载红边波段的卫星载荷越来越多,即将发射的国产卫星也拟增加红边波段提高作物识别能力,该文研究结果将为国产红边卫星数据在农业上的应用提供参考。

       

      Abstract: Adding red-edge waveband (690-730 nm) based on traditional visible light and infrared band is a notable trend of the development of current high resolution satellite sensors. RapidEye satellite carries red-edge waveband sensors. Based on the RapidEye satellite remote sensing data of Dongsheng town, Bei′an city, Helongjiang province on July 27, 2014, and by employing the monitoring classification method, this paper comparatively analyzed the impact of the red-edge waveband on the estimation accuracy of crop planting area under 2 kinds of waveband combinations. The indices including the separable measure, the classification accuracy and the degree of landscape fragmentation of the 3 kinds of ground objects i.e. corn, soybean and the others were computed under the conditions of 2 types of band combinations, which were with or without the involvement of red-edge waveband. Training samples of monitoring classification took the 2 km × 2 km grids covering study area as their basic units. Under the principle of equal probability of corn and soybean area proportion, 10 grids were chosen as training samples. Identification of crop within ground samples employed visual interpretation method. Accuracy verification adopted the background survey results of the crop area covering the study area. Based on the preliminary classification of RapidEye data with spatial resolution of 5 m, the background survey was conducted by using visual observation correction method combined with ground survey according to the seasonal changing rule of multi-temporal Landsat-8/OLI (Operational Land Imager) data. The result showed that, the overall identification accuracy of 3 types of ground objects (corn, soybean and the others) with red-edge was 88.4%, the Kappa coefficient was 0.81, and the mapping accuracies of 3 types of ground objects were 93.1%, 86.0% and 87.3% respectively; the overall identification accuracy of 3 types of ground objects without red-edge was 81.7%, the Kappa coefficient was 0.71, and the mapping accuracies of 3 types of ground objects were 83.9%, 73.4% and 84.6% respectively. By introducing red-edge band, the overall identification accuracy of 3 ground objects was improved by 6.7%, and the identification accuracies of 3 types of ground objects were improved by 9.20%, 12.6% and 2.7% respectively. By employing Jeffries-Matusita method, we calculated the degree of separation of 3 types of ground objects. The degrees of separation between corns and soybeans, corns and the others, as well as soybeans and the others were improved from 0.84 to 1.73, from 1.37 to 1.81, and from 1.27 to 1.29 respectively; by employing fragmentation index, we calculated the landscape fragmentation. The number of land parcels was reduced by 69.2%, with the average parcel area increased by 2.2 times, the average parcel perimeter increased by 60.5%, and the ratio between parcel area and perimeter increased by 1.0 time. So, by introducing red-edge band, the study has improved the separable measure of different ground objects, reduced the increase of landscape fragment caused by "Pepper salt" effect, and improved the overall identification accuracy of crop planting area. Currently, more and more satellites carry red-edge devices, and the domestically-produced satellites to be launched also plan to add red-edge band so as to improve crop identification capacity. The result of this paper will provide a reference for the application of domestically-produced red-edge satellite data in agriculture.

       

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