Study On Monitoring Wind Sand Movement In Mogao Grottoes Based On InSAR

The conservation of cultural relics is not only about the conservation of the cultural relics themselves,but also about the overall protection of the ecological environment of cultural relics.The impact of natural climate on cultural relics has always been a concern for the conservation of cultural relics.How to combine the preservation status and preserving environment of heritage sites and carry out targeted preventive protection based on relevant monitoring results is currently a difficult problem that needs to be urgently solved.The sand wind issue of Mogao Grottoes is due to the special preserving environment characteristics.Sand accumulation at the top of the cliff,wind erosion on the cliff faces,and dust inside the caves threaten all aspects of the Mogao Caves.Traditional monitoring methods of wind and sand,such as wind ladder station and sand meter not only cost a lot of time and effort,but also limited monitoring range.Synthetic aperture radar interferometry has the characteristics of all-weather,wide range and high precision,which provides a new technical means for the monitoring of wind-sand migration in Mogao Grottoes area.Based on Sentinel-1 data provided by ESA,this research takes Mogao Grottoes area in Dunhuang as the research object,In order to study the wind sand movement characteristics of the Mogao Grottoes area,InSAR technology was used in this research based on Sentinel-1 data provided by ESA.The deformation monitoring of Mogao Grottoes area is carried out by D-InSAR and SBAS-InSAR techniques respectively.The laws of wind-sand movement at the top of grottoes are revealed preliminarily by combining field investigation and verification.A deformation monitoring method combined D-InSAR and SBAS-InSAR technology is proposed,which can effectively monitor the surface deformation caused by wind sand and other factors in Mogao Grottoes area.The main research results are as follows:(1)The wind field characteristics of the Mogao Grottoes area from 2014 to 2022 were analyzed.The frequency of various wind directions and the annual average wind speed,maximum wind speed,maximum meridional wind speed and maximum zonal wind speed were counted.The annual wind direction rose diagram and the sediment transport potential rose diagram were drawn.It was found that the Mogao Grottoes area was mainly in the south,northwest and northeast directions of sediment transport,which belonged to the medium wind energy environment.(2)D-InSAR technology can be used for sand monitoring after strong wind events in Mogao Grottoes.The windy weather on June 13,2019 was taken as an example.The main wind direction was westerly.The zonal wind speed after decomposition was 7.27 m / s,and the maximum wind speed was 20.74 m / s.According to the monitoring results,the A-shaped sand control network area on the top of the Mogao Grottoes was obviously accumulated during the windy weather,and the maximum accumulation amount was 2.5 mm.Taking the gale weather on April10,2020 as an example,the main wind direction is east wind.The zonal velocity after decomposition is-14.04 m/s,and the maximum wind speed can reach 25.6 m / s.The monitoring results show that the influence of east wind on the accumulation of wind sand on the top of Mogao Grottoes is relatively small,and the overall deformation is relatively uniform.(3)SBAS-InSAR technology has high reliability in sand monitoring in Mogao Grottoes,and can also be used for other deformation monitoring in Mogao Grottoes.Based on the SARSCAPE plate under the ENVI platform,the deformation monitoring of the Mogao Grottoes area was carried out by using the Sentinel-1 ascending and descending orbit data of the ESA.The results of the ascending orbit showed that the annual average deformation rate of the Mogao Grottoes area was-9-8mm/y,and the cumulative deformation was between-30-35 mm.The results of the descending orbit showed that the annual average deformation rate of the Mogao Grottoes area was-8-6mm/y,and the cumulative deformation was between-30-30 mm.Finally,the reliability of SBAS-InSAR results is further illustrated by using RMSE,average coherence coefficient and cross-checking of ascending and descending orbits.(4)Based on the ascending orbit data and descending orbit data combined with the principle of two-dimensional surface deformation solution,the two-dimensional surface deformation of Mogao Grottoes is extracted.The relevant deformation information in the vertical and east-west directions of the Mogao Grottoes was obtained,in which the cumulative deformation range in the vertical direction was-34-20 mm,and the cumulative deformation range in the east-west direction was-38-43 mm.According to the field verification,relevant meteorological data and two-dimensional deformation calculation results,the causes of deformation in Mogao Grottoes are divided into natural factors and human factors.The natural factors include the erosion and accumulation of wind-blown sand and the erosion and accumulation of Daquan River.The erosion of wind-blown sand mainly occurs in the grass grid area,and the accumulation of wind-blown sand mainly occurs near the A-shaped sand-proof net,the east bank of Daquan River and the west side of 217 line highway.Human factors include the repair of Mogao Grottoes and artificial site excavation.