基于气象和覆被条件考量的无人机地形勘察适宜期——以东北黑土区为例

Investigating optimal time window for UAV terrain measuring by considering weather and land cover conditions:Taking the Northeast Black Soil Region as an example

基于无人机平台的SfM技术是获取高精度地形的重要手段,如何在开展外业测量之前确定地形勘察的最佳日期对水土保持项目的规划和实施至关重要。以东北黑土区不同气候带为例,结合当地的气候和植被动态变化特征探讨该区适宜无人机地形勘察的最佳时间窗口,以期为其他地区的地形勘察期选取提供借鉴,为水土保持领域的地形侵蚀监测研究服务。选择的试验区东北黑土区跨寒温带、中温带和暖温带3个温度带,分析不同温度带典型站点1988—2017年的气候数据以及2020年全年的植被覆盖度、雪盖变化;以常见的大疆无人机运行参数作为气候数据的筛选条件,初步按照中覆盖(FVC<0.6)条件为植被覆盖度的筛选依据,确定无人机地形勘察的适宜期。结果表明:东北黑土区3个温度带进行无人机地形勘察的最适时间范围分别是:寒温带的适宜时间为4月中旬至5月初、中温带为4月中旬至5月中旬、暖温带为3月中旬至4月底和9月底至11月初。

[Background]The Structure from Motion(SfM)technology based on the Unmanned Aerial Vehicle(UAV)platform is an important optical remote sensing technology to measure high-precision digital terrain.The SfM technology is often influenced by clouds and vegetation cover,whereas the UAV platform could be impacted by winds.This work aims to explore the optimal time window to measure terrain by the UAV-SfM survey in the Black Soil Region of Northeast China by considering dynamic changes of local climate and vegetation.[Methods]The study area covers three climatic zones:The cold temperate zone,the middle temperate zone and the warm temperate zone.For different climatic zones in the Black Soil Region of Northeast China,the climate data of a typical site from 1988 to 2017 and the dynamics of vegetation coverage and snow cover in 2020 were analyzed.Typical DJI UAV operating parameters were used as the initial screening conditions for annual average climate data(temperature,wind speed and precipitation),and the medium vegetation coverage condition(FVC<0.6)was then used as the screening basis for vegetation coverage to determine the appropriate period for the UAV terrain survey.[Results]1)The temperature and wind speed of the three meteorological stations were analyzed comprehensively.It was found that the temperature curve changed as a quadratic function,and the average wind speed curve and the maximum continuous wind speed curve had the same trend.Temperature and wind speed were satisfied in the cold temperate zone from mid-April to early October,in the middle temperate zone from early April to mid-October,and in the warm temperate zone from mid-March to mid-November.2)The probability of daily precipitation curves in the three meteorological stations fluctuated greatly and were not significantly representative,thus it could not be used as the standard for estimating investigating optimal time window.3)By analyzing the land cover conditions of the three sites,it was found that the ground was covered with snow from October to March of the following year,and the vegetation coverage exceeded 0.6 from May to October,which made it impossible to carry out UAV topographic survey.The cover conditions that met terrain acquisition range from March to the end of April and from the end of September to November.Comprehensive analysis of meteorological and cover conditions,we found that the most suitable periods for the cold,middle and warm temperate zones were from mid-April to early May,from mid-April to mid-May,and from mid-March to the end of April or from the end of September to the beginning of November.[Conclusions]By applying the results of this paper,the UAV-SfM survey may effectively avoid adverse periods and ensure obtaining the best results.The findings of this work could guide terrain measuring works in the field of soil and water conservation.