The annual cycle of precipitable water vapor is inferred from the MODIS thermal infrared (IR) and nearinfrared (NIR) satellite products under clear-sky conditions and for the period 2002-2008 at 18 sites of the Iberian Peninsula, with the aim to evaluate the capabilities of both algorithms. The paper presents these results in relation with ground observations using different techniques (GPS, sunphotometer, radiosounding), with a special emphasis on GPS. The differences in the monthly means mostly correspond to underestimations, ranging between a few percent to 40%, being generally larger in winter than in summer. For most sites, NIR performs better than IR, and more particularly during the winter. NIR usually presents overestimations in summer that can reach up to 30%. The time-coincident comparison shows that best MODIS/GPS agreement is found for the continental region (rms∼0.3) for both methods, whereas the largest biases and rms differences are found at the Mediterranean sites.

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