Data Products  › Product & Algorithm › Caveats of Integrated Water Vapor product
In order to utilize AMSR and AMSR-E data, product format and algorithm overviews, how to access products, and useful tools for display and analysis them are introduced.

Caveats for the standard products

Caveats of Integrated Water Vapor product

Algorithm development PI: Dr. Yoshiaki Takeuchi (Japan Meteorological Agency)

This document briefly describes some caveats for the AMSR Level 2 standard products of integrated water vapor.
Retrieval areas
Values of integrated water vapor are retrieved over global oceans (except over sea ice) in this product. Land areas are masked out by using land-ocean flag information based on the GTOPO30 database. Sea ice areas are excluded by referring the AMSR Level 3 sea ice concentration product. In addition, retrieval is not performed in the regions where sea surface wind speeds exceed the value of 20 m/s or the input brightness temperatures are bad in quality. Retrieval may be performed over large lakes.

Retrieval range and error
Range of the water vapor retrieval is between 0 and 70 kg/m2. Retrieval error was estimated within 2.5 kg/m2 by using match-up dataset of radiosonde-derived water vapor and AMSR estimates.

Quality flags are included in the product, indicating the categories of clear, cloudy, heavy rain, and low quality. Quality with the retrieval error within 2.5 kg/m2 is applicable for the data with clear category flag. Data qualities of the estimates in other categories are inferior to that of clear category. Therefore, users must select the data depending on their purpose.

Estimates in heavy rain category
In the version 1.0 product, values of integrated water vapor are set to -999.9 in the heavy rain category. This is due to the insufficient match-up dataset with radiosondes for computing retrieval coefficients under heavy rain category.

Ancillary data used in retrieval
In course of the retrieval, sea surface wind speeds, 850hPa air temperatures, and sea surface temperatures (SST) are used as ancillary input data. Values of sea surface wind speeds and 850hPa air temperatures are obtained by interpolating (in space and time) the global analysis (GANAL) and forecast data provided by the Japan Meteorological Agency (JMA). Three-days average of AMSR Level 3 SST is used as SST ancillary information. Climatological SST values are used as an alternative in the regions where the AMSR Level 3 SST is not available (e.g., near coast lines).