Abstract

Water vapour is highly variable over tropical region and sensitive to weather condition, monsoon onset, green house effect, and pollution level in Ganga River. In the present study, variability in water vapour derived from Global Positioning System (GPS) over Varanasi (25°20′N, 82°59′E) during the period 2007–2010 has been studied. The GPS-derived water vapour (WV) has been compared with those retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) and ECMWF. The GPS-WV data concurrent to MODIS and ECMWF timing has been correlated to perform further analysis. To study the accuracy of water vapour retrieved from the MODIS and ECMWF, root mean square error (RMSE), absolute error (AE), correlation and standard deviation in it are computed with respect to GPS-derived water vapour. Analysis shows an annual correlation R² = 86%, RMSE = 9.5 mm and AE (MODIS–GPS) = 7.0 mm in MODIS retrieval and annual correlation R² = 86%, RMSE = 6.1 mm and AE (ECMWF–GPS) = 2.4 mm in ECMWF reanalysis retrieval. Correlation of ECMWF and MODIS datasets with the GPS datasets are found to vary significantly with seasons. The correlation is high during monsoon season and low during spring season. Water vapour is found to be an indicator for the onset of monsoon.

Research Highlights

• Accuracy of water vapor (WV) retrieved from the MODIS and ECMWF with respect to GPS WV.

• High Annual correlation of R2 = 0.86 between both MODIS–GPS and ECMWF–GPS.

• The correlation is high during monsoon season and low during spring season.

• The performance of ECMWF is found to be better than that of MODIS.

中文翻译：

---

从MODIS和ECMWF提取水蒸气的性能及其在瓦拉纳西的地面GPS测量的验证

摘要

水汽在热带地区变化很大，并且对恒河的天气状况，季风发作，温室效应和污染水平敏感。在本研究中，研究了2007-2010年期间瓦拉纳西（25°20′N，82°59′E）上全球定位系统（GPS）产生的水蒸气的变化性。已将GPS衍生的水蒸气（WV）与从中分辨率成像光谱仪（MODIS）和ECMWF中检索到的水蒸气进行了比较。已将与MODIS和ECMWF时序同时存在的GPS-WV数据关联起来以执行进一步的分析。为了研究从MODIS和ECMWF中检索到的水蒸气的准确性，针对GPS衍生的水蒸气计算了均方根误差（RMSE），绝对误差（AE），相关性和标准偏差。分析显示年度相关性 在MODIS检索中，R ² = 86％，RMSE = 9.5毫米，AE（MODIS–GPS）= 7.0毫米，年相关性 在ECMWF重新分析检索中，R ² = 86％，RMSE = 6.1毫米，AE（ECMWF–GPS）= 2.4毫米。发现ECMWF和MODIS数据集与GPS数据集的相关性随季节显着变化。相关性在季风季节高，而在春季低。发现水蒸气是季风发作的指标。

研究重点

• 从MODIS和ECMWF获得的相对于GPS WV的水蒸气（WV）的精度。

• MODIS–GPS和ECMWF–GPS之间的R2的高年度相关性= 0.86。

• 相关性在季风季节高，而在春季低。

• 发现ECMWF的性能优于MODIS。