The Time Series of Terra and Aqua MODIS Near-IR Water Vapor Products

Two Moderate Resolution Imaging SpectroRadiometer (MODIS) instruments [1] on the NASA Terra and Aqua Spacecraft platforms are currently operational for global remote sensing of the land, ocean and atmosphere. Both MODIS instruments are equipped with channels located within and around the 0.94-micron water vapor band absorption region for water vapor measurements over reflective land surfaces, clouds, and oceanic regions with sunglint. We have developed an algorithm to retrieve column water vapor amount using ratios of water vapor absorption channels with nearby atmospheric window channels [2]. The daily `pixel-based´ Level 2 near-IR water vapor product at the 1-km spatial resolution of the MODIS instrument, and the daily, 8-day, and monthly-mean Level 3 near-IR water vapor products at a 1deg by 1deg latitude-longitude grid globally are routinely produced at a NASA computing facility [3]. We have analyzed more than eight years of Terra MODIS and five years of Aqua MODIS Level 3 monthly-mean near-IR water vapor products. Major observations on spatial distributions and temporal variations of water vapor in different geographic regions are described in this paper. Areas severely affected by the 2002 El Nino phenomenon in southeastern Australia and southeastern Asia can be detected from the Level 3 monthly-mean data sets. The 2007 drought areas in southeastern US can also be seen. It is concluded that the MODIS near-IR water vapor products can be useful for establishing a long term water vapor climatology over global land surface areas.