| Soil water is an indispensable part of ecosystem maintenance.Due to the unique binary three-dimensional spatial structure system in karst area,the surface soil water is especially precious,which is of great significance for the monitoring of soil water in karst areas.The study takes the karst plateau gorge area affiliated to the Guanling-Zhenfeng Huajiang Demonstration Zone as the research object.Based on the Sentinel-1A and Landsat 8 OLI remote sensing images,the influence of surface vegetation layer on soil water remote sensing monitoring is eliminated through the ‘water cloud model'.Based on field measured data,a soil water remote sensing inversion model was constructed.Using the combination of different polarization modes and different index parameters in multi-source remote sensing,the inversion results of different combinations are obtained by comparing the overall data inversion.Combined with different combinations of different coverage methods,more comprehensive inversion results are obtained and compared.The best combination method in the soil water content inversion model is obtained by analysing,and the accuracy is verified.Inversion of the overall soil water content distribution in the study area,combined with different seasons and different rock desertification grades,the spatial and temporal changes of soil water content in the study area were analyzed.The results showed that:(1)‘Water-cloud Model'can better remove the influence of vegetation layer on soil water inversion.The soil backscattering coefficients based on Sentinel-1VV polarization and VH polarization inversion were inverted with the three indices calculated by Landsat 8 OLI data.Comparing the results of the six models,it is found that the VV polarization inversion effect is better than VH polarization under different polarizations.Among them,VV+NDVI,VV+NDWI,VV+NDWI2 inversion results are very similar,and the fit between the backward scattering coefficient and the actual soil moisture content obtained by VV+NDWI2 model inversion is relatively high,the fitness R= 0.59,the VV+NDVI inversion results were second,the fitness was R=0.58.The V values of VH+NDVI,VH+NDWI,VH+NDWI2 are lower after inversion.(2)According to the coverage of surface vegetation in the study area,the study area is divided into three major areas: low coverage(naked land,reclaimed land),medium coverage(land,grassland,low shrub,etc.),high coverage(forest land,high-density shrubs).At the same time,the sampling points were fitted and analyzed according to different coverage and different vegetation types.The results showed that VV+NDVI was the most stable under different coverage,and the R value was 0.66.(3)Dividing the proportion of water content in the surface layer of the study area into 7 layers: 0~10%,10~20%,20~30%,30~40%,40~50%,50~60%,>60%,the water content in the surface layer of the soil is 30-40% in most areas,and the area with higher soil water(except water)is mainly distributed in low altitude areas,while the soil moisture content at the top of the mountain is at Below 20%;in addition to the influence of altitude,the soil moisture around the valley is higher,which is perpendicular to the elevation gradient.The spatial pattern has the dual effects of gradient change with altitude and distribution of different micro-geomorphology types.Compared with different seasons,the overall soil water content in September was higher,and the area increased in 50~60% and >60% stratification compared with other months.In June,the soil water content was more dispersed than other months.(4)According to the analysis of the change of soil water content according to the degree of rocky desertification,it is found that there are obvious change characteristics.The soil water content of non-rocky desertification,latent rocky desertification,mild rocky desertification and moderate rocky desertification ranged from 20% to 50%,and in some areas the soil water content ranged from 50% to 60%.Severe rocky desertification,extremely strong rocky desertification,relatively dispersed water content.Non-karst region soil water content is relatively high and relatively stable,mainly distributed between 30% and 50%.(5)Exploring the variation characteristics of different rocky desertification control projects and soil water content under different seasons,it is found that in the karst rocky desertification areas where the ecological environment is extremely fragile and easy to destroy and difficult to repair,the rocky desertification of human intervention is particularly important.Among them,the seasonal changes of soil moisture content of shelter forests and slope-changing ladders are relatively stable;the soil water content of artificial grassland,water-protected forest and fruit-bearing forests varies with seasonality and human disturbance;the closure of mountainous forestry areas is affected by seasonality,at a certain time.There is still a need to strengthen protection.. |
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