MODIS infrared (IR) water vapor calibration model and assessment

Moderate Resolution Imaging Spectroradiometer (MODIS) can monitor precipitable water vapor (PWV) with high accuracy and large scales over land and ocean, using both near-infrared (nIR) bands and traditional IR bands. The MODIS nIR PWV is only available during daytime, which can be retrieved at 1×1km spatial resolution with high accuracy, while the MODIS IR PWV can be obtained during both the day and night time with a lower spatial resolution (5×5km), but is less accurate than the nIR PWV. In this paper, the performances of MODIS water vapor products at IR and nIR bands are evaluated by comparing with ground continuous GPSobservations. Results show that the traditional linear regression analysis is not the best choice to calibrate the MODIS PWV from the IR band. A new calibration model is being developed for the MODIS IR water vapor product using the IGS and radiosonde observations within the MODIS image coverage, and calibrated results are presented and assessed.