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Data Quality of AIRS Level 2 Standard Products*

Data Quality of AIRS Level 2 Standard Products*. Not all L2 data values are of equal quality quality varies for the same parameter in different retrievals quality can vary for different parameters in the same retrieval

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Data Quality of AIRS Level 2 Standard Products*

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  1. Data Quality of AIRS Level 2 Standard Products* • Not all L2 data values are of equal quality • quality varies for the same parameter in different retrievals • quality can vary for different parameters in the same retrieval • Quality Assurance variables in the files provide separate physical product quality information for individual retrievals • Three levels of quality are identified: 2 = “Do Not Use” 1 = “Good”, e.g., usable for climate studies 0 = “Best”, recommended for data assimilation * AIRX2RET, AIRS2RET, AIRH2RET

  2. Using Bad Quality Data Can Affect Your Results Total Column Precipitable Water Quality Best Do Not Use Good kg/m2 The unusually dry pixels on the east side of Hurricane Ike (arrow) have “Do Not Use” quality flags.

  3. How to Filter Data by Quality Criteria • Option 1: Write your own software to do it • This can be daunting for first-time AIRS users • Some relationships between quality assurance criteria and data are complicated • Option 2: The Data Quality Screening Service* • DQSS is an on-the-fly service which excises data which do not meet the desired quality • Screening criteria can be based on • default AIRS Science Team Recommendations (for climate studies) • the more restrictive recommendation for data assimilation • or your own custom selections, variable by variable *DQSS is funded by NASA’s ACCESS Program

  4. DQSS Filters Bad-Quality Pixels from the Data Original data array (Total column precipitable water) Mask based on user criteria (e.g., Quality level < 2) Good quality data pixels retained Output file has the same format and structure as the input file (except for the extra arrays with the mask and original values)

  5. Visualizations are Provided to Allow Usersto See the Effect of Different Quality Filters Best quality only Best + Good quality

  6. Basic Flow of Screening Process • Search for data through Mirador* • View Files • Select files and Add to Cart • Apply Quality Screening service • Select screening criteria • Continue to cart • Checkout to get a list of URLs for screened data • Download URLs Screening is applied with each download *http://mirador.gsfc.nasa.gov

  7. DQSS is Available via the MiradorSearch Tool: http://mirador.gsfc.nasa.gov Search on “AIRX2RET”

  8. From “Data Sets” page, drill down on “View Files”...

  9. From the File Listing, there are 2 waysto screen: individually or as a batch BATCH: Click checkboxes to select files.Then click “Add Selected Files To Cart”. INDIVIDUALLY: Click on “HDF (Quality Screened)” This begins screening (using science team recommendations) and then downloading to your machine.

  10. Batch mode:Select “Quality Screened HDF” under “Available Services”

  11. Then select quality screening criteria... Initial settings are based on Science Team recommendation. (Note: “Good” retains retrievals that Good or better). You can choose settings for all parameters at once... ... or parameter by parameter.

  12. Next, click “Continue to Shopping Cart”... Note that “Quality Screened HDF” is now the Selected Service

  13. Continue to “Checkout”...

  14. Click “URL List (Data)” for a list of the quality screen URLs...

  15. Finally... • Save the URL list to a file, e.g., “urls.txt” • Run “wget --content-disposition -iurls.txt” • downloads screened files to current directory* • Each file is screened as it is downloaded • Each one takes about 25-30 sec. to screen • Screened files are ~25-30% larger than original • Original data array and quality control mask are also included • *Add “-P <dir>” to specify directory

  16. Coming Soon... • DQSS for more A-Train datasets • MODIS Level 2 atmospheres • MLS Level 2 • OMI Level 2 • HIRDLS Level 2

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