Intercomparison of total precipitable water measurements made by satellite‐borne microwave radiometers and ground‐based GPS instruments

High‐quality, high temporal resolution measurements of total precipitable water (TPW) can be made by evaluating the vapor‐dependent delay of radio signals reaching land‐based Global Positioning System (GPS) receivers from GPS satellites. These measurements are available since the mid‐1990s when the GPS system became operational. Over the world's oceans, satellite‐borne microwave imaging radiometers have been making measurements of TPW for more than 25 years. In this work, we perform an intercomparison of collocated TPW measurements made by these two disparate systems using measurements from 26 GPS stations located on small islands. The two types of measurements agree well, with typical satellite‐station mean differences of less than 1.0 kg m −2 . Analysis revealed several cases of inhomogeneities in the GPS data set, and two deficiencies in the Remote Sensing Systems satellite data, demonstrating the usefulness of intercomparison for improving the accuracy of both types of data. After the individual station, biases were removed, the standard deviation of the overall differences between individual satellites and GPS measurements ranged between 1.60 and 1.94 kg m −2 . Twelve GPS stations had overlap time periods long enough to evaluate difference trends, yielding 59 satellite‐station pairs when paired with different satellites. More than half of the pairs (39 of 59) did not show a significant trend. The 20 pairs with significant trends did not show trends of predominantly one sign, suggesting that neither system is plagued by a system‐wide drift in TPW.