The Data Quality Screening Service filters bad-quality data points from a data file using quality variables included within the file. The service is available through the Mirador search tool. It generates output files that have the same structure as the input (albeit with a few extra variables) and is thus usable in any tool made to work with the original product. The service replaces data objects (arrays) with the corresponding screened (filtered) data arrays. Data values deemed unusable are set to Fill Values. The output file also includes the quality mask used for filtering and the original (unscreened) data values in additional data objects. There will also be a file-level metadata object describing what was done in the quality screening process.
The figure above shows an AIRS data variable from one swath file before screening on the left. The Quality Mask shows data points (white) with quality classified as “Good” or “Best” (following the recommendation of the AIRS Science Team), with black indicating “Do Not Use”. The data layer After Screening retains only the values classified as “Good” or “Best”, with Fill Values (black in viewed images) occupying the rest.
How To Use the Data Quality Screening Service
The Data Quality Screening Service is available through the Mirador Search tool for:
- AIRS Standard Retrieval (Version 5, also known as AIRX2RET.005, AIRS2RET.005 or AIRH2RET.005)
- MLS Water Vapor (Version 3, also known as ML2H2O.003).
- MLS Ozone (Version 3, also known as ML2O3.003).
Search on Keyword (e.g., AIRX2RET, ML2O3 or ML2H2O) to get a dataset list and then the "005" link to View Files. From the File Listing page for one of these products, you can invoke the service immediately for individual files by clicking on the "HDF (Quality Screened)" link.
The process takes about 20 seconds to run and will download an AIRS file with the same name as the original, prefaced by "QC_", e.g., QC_AIRS.2010.03.31.070.L2.RetStd.v220.127.116.11.G10091061738.hdf. MLS files take only a few seconds.
Batch Downloads and Custom Screening Criteria
If you want to apply the service in batch, OR use something other than the default recommended criteria, then add the selected files to the Shopping Cart. In the Shopping Cart page, select the service "HDF (Quality Screening)". This will bring up a screen allowing you to set individual criteria by variable, as well as to visualize the effect that different screening scenarios will have on the data. After you make your selections, click Submit. Click Continue to the Shopping Cart and then click Checkout in the next screen. In the Checkout screen, click URL List (Data) to get the list of URLs to apply the DQSS in batch. As you fetch each URL, the DQSS will be applied on the fly.
More Information on Quality
More information on the use of AIRS Quality information is available in AIRS/AMSU/HSB Version 5 Level 2 Quality Control and Error Estimation (pdf).
A DQSS also exists for MODIS Aerosols and MODIS Water Vapor products, which are available as a post-processing on demand option through the LADSweb search interface.