| Soil moisture is an important parameter in the fields of agriculture,soil science,and environmental science.Passive microwave remote sensing has become one of the most effective methods for continuous monitoring of soil moisture on a large scale.The QinghaiTibet Plateau is known as the third pole of the earth.It is the highest and largest plateau in the world.It has an important impact on the global climate.At the same time,the Qinghai-Tibet Plateau is also one of the most sensitive areas to climate change.At present,the accuracy of microwave remote sensing inversion of soil moisture in the Qinghai-Tibet Plateau is low,and there is a problem that the generalization of the algorithm is not strong.Therefore,this paper selects the brightness temperature data provided by the AMSR2 sensor mounted on the GCOM-W1 satellite,and uses the improved Qp(No Roughness Parameter)algorithm to retrieve soil moisture in the Qinghai-Tibet Plateau,and uses Maqu and Pali observations The measured data of the network and the two existing AMSR2 soil moisture products verify and evaluate the inversion results.The main research contents and conclusions of the thesis are as follows:(1)Improve the surface temperature model in Qp algorithmAiming at the problem of low accuracy in inverting the surface temperature of the Qinghai-Tibet Plateau using the single-channel method in the Qp algorithm,a four-channel surface temperature inversion model based on K-band dual-frequency and dual-polarization is used for the Qinghai-Tibet Plateau region for the three years 2016～2018 Inversion and verification of surface temperature.The verification results using the measured surface temperature of the two weather stations of Naqu and Maqu at 0cm and the observation network of Naqu and Pali at 5cm have proved that the inversion results based on the fourchannel temperature model have higher accuracy.The average deviation of Naqu Meteorological Station is-3.951℃,which is 8.205℃ less than that of the original model,and the root mean square error is 6.032℃,which is 4.190℃ less than that of the original model.The correlation of Maqu weather station reached 0.87,with an average deviation of-0.049℃,which was 1.352℃ less than the original model.The correlation of the Naqu Observation Network at the time of orbit drop is as high as 0.91,the average deviation is4.103℃,which is 6.322℃ less than the original model deviation,and the root mean square error is 5.527℃.The correlation of the Pali Observation Network is as high as 0.96,the minimum average deviation is-4.754℃,and the minimum unbiased root mean square error is 1.656℃.The improved surface temperature model has improved the accuracy of ground temperature estimation in the Qinghai-Tibet Plateau.(2)Inversion of soil moisture in the Qinghai-Tibet Plateau based on the improved Qp algorithmThe improved Qp soil moisture algorithm was improved by using the improved land surface temperature inversion model and the vegetation index average data set with a time resolution of 10 days was introduced.The Qp algorithm before and after the improvement was used to invert the soil moisture in the Qinghai-Tibet Plateau.The results show that,compared with the original Qp algorithm,the inversion result of the improved Qp algorithm is closer to the true value.From the comparison of time series,it has a higher degree of coincidence.The correlation coefficient of the Naqu observation network is as high as 0.83,and the average deviation,root mean square error,and unbiased root mean square error at the time of orbit ascent are all reduced to a certain extent;Parry The correlation of the observation network reaches 0.75,the minimum average deviation is-0.037m~3/m~3,and the root mean square error is 0.050m~3/m~3.The verification results show that the overall accuracy of the improved Qp algorithm in the Qinghai-Tibet Plateau is better than the original Qp algorithm.(3)Verification and evaluation of Qp improved algorithm soil moisture inversion resultsIn order to further verify the applicability of the improved Qp algorithm in soil moisture retrieval in the Qinghai-Tibet Plateau,the results of the improved Qp algorithm inversion were compared with the existing JAXA AMSR2 and LPRM AMSR2 soil moisture products.The results show that the improved Qp algorithm’s soil moisture inversion results have a higher correlation coefficient than the two soil moisture products of JAXA and LPRM in the Qinghai-Tibet Plateau,up to 0.83.At the time of orbit,the minimum average deviation is-0.007m~3/m~3;the root mean square error of the two soil moisture products of JAXA and LPRM are both greater than 0.084m~3/m~3,and the root mean square error of the Qp improved algorithm inversion result is less than 0.084m~3/m~3,The minimum value is 0.050m~3/m~3.Therefore,the improved Qp algorithm inversion has certain advantages compared with similar products.In summary,the improved Qp algorithm with the introduction of the K-band dualpolarization four-channel temperature inversion model has significantly improved the accuracy of soil moisture inversion in the Qinghai-Tibet Plateau,and the applicability is stronger. |
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