Terrain height assessment of satellite laser altimetry standard products for natural resources
Satellite laser altimetry technology,with its ability to acquire highly accurate vertical distribution information,possesses unique advantages in the field of Earth observation.Currently,different satellite laser altimetry systems are operating in orbit both domestically and internationally.In recent years,China has launched the GF-7 satellite and ZY3-03 satellite,both equipped with laser altimetry systems,which are primarily employed for acquiring global laser elevation control points.With the steady operation of these satellites in orbit and the continuous acquisition of laser altimetry data,China has,for the first time,formed related data products in the field of laser altimetry,called Satellite Laser Altimetry standard(SLA03)data products for natural resources.To better understand the accuracy level of the products and guide the subsequent application and optimization,a comprehensive accuracy evaluation must be conducted.Based on the high-accurate airborne LiDAR data gathered in plain areas and mountainous regions with forests,thousands of laser points are collected to comprehensively evaluate the terrain height accuracy of the SLA03 data products for natural resources in this paper.After coordinate transformation and data conversion,the SLA03 data and reference data are unified into the same coordinate framework.Then,taking the size of the laser ground spot into consideration,the reference terrain elevations are obtained based on the points classified as ground from the LiDAR data.Multiple accuracy metrics,including overall bias,Mean Absolute Error(MAE),Root Mean Square Error(RMSE),and 90th percentile Linear Error(LE90),are utilized for elevation accuracy assessment.Results show that,after eliminating the laser points located at tree canopies or buildings using a proper threshold,the height accuracy of the SLA03 data products from the GF-7 satellite is 0.653 m in RMSE and 1.055 m in LE90 in plain areas,with over 60％under 0.3 m,but decreases to 1.210 m(RMSE)and 2.002 m(LE90)in mountainous regions with forests.The accuracy of the SLA03 data products from the ZY3-03 satellite is 1.312 m(RMSE)and 2.389 m(LE90)in plain areas with more than 50％under 0.5 m,while in the mountainous regions with forests,it declines to 1.661 m(RMSE)and 2.999 m(LE90).The potential for elevation control points in the plains is above 60％for both the GF-7 and ZY3-03 satellites,but additional screening is required before use.The elevation accuracy of SLA03 products from the GF-7 satellite is obviously affected by seasonal factors,which are mainly caused by vegetation growth.Meanwhile,the elevation accuracy of SLA03 products from the ZY3-03 satellite is inferior to that of the GF-7 satellite,hindering the former satellite from effectively distinguishing the impact of seasonal changes in vegetation.The relevant conclusions will guide the effective application of SLA03 products and provide support for the design and parameter argumentation of subsequent satellite laser altimetry systems.
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