The Atmospheric Infrared Sounder (AIRS) Version 6 Level 2 processing code is now used to produce AIRS Near Real Time (NRT) Level 2 products. AIRS Version 6 Level 2 data represent a significant improvement over the Version 5 products. Details on the changes in the Version 6 Level 2 products can be found in the Version 6 Release Announcement and on the Version 6 Documentation Page. The NRT Level 2 data are produced with the same processing code as the standard products with up to 4 differences in the processing to satisfy the latency requirements for NRT data. The differences in NRT processing include:
- The NRT granules are produced without previous or subsequent granules if those granules are not available within 5 minutes (previous and subsequent granules are used for calibration and are generally present in 5 minutes).
- Predictive ephemeris/attitude data are used (in contrast, definitive ephemeris/attitude data are used for processing standard products).
- Nominally, a forecast surface pressure is used; if this is unavailable, a surface climatology is then used.
- No ice cloud properties retrievals are performed (ice cloud properties are a new retrieval in the Version 6 support product AIRX2SUP).
These differences in processing between NRT data and standard products are virtually the same as with Version 5. Their effect on the retrievals is usually minimal and is described in the Guide to AIRS Near Real Time Data. No changes have been made to the Level 1B NRT products, which are still produced with Version 5 code.
The latency of the Version 6 Level 2 products is within the 3 hour requirement for Land Atmosphere NRT Capability for Earth Observing System (LANCE) products, and only slightly different than that of the Version 5 products. A four week test period shows that 99.0% of the AIRS Version 6 Level 2 NRT data products have been available to users within 3 hours of observation, with an average latency of 2 hours 5 minutes. These figures compare favorably with Version 5 Level 2 Near Real Time products, where 99.8% of products were available within 3 hours of observation with an average latency of 1 hour 40 minutes.
The AIRS NRT products are freely available by ftp from two mirrored servers, discnrt1 and discnrt2. Access requires registration with EOSDIS (NASA's Earth Observing System Data and Information System). Information about all of the AIRS NRT products is on the AIRS NRT Data Holdings Page.
Some of the improvements in the AIRS Version 6 data are shown in the headline image at upper right) (granule 77 from March 18, 2013) which shows the improved resolution of the AIRS Version 6 cloud top pressure. Figure 1 (below) shows a comparison of global maps of carbon monoxide (CO) derived from AIRS Version 5 and Version 6 NRT processing. Images of several variables derived from AIRS NRT observations can be viewed using the GES DISC MapViewer or using Web Map Service (WMS)/Web Coverage Service (WCS) capable tools such as GoogleEarth.
NRT granules of interest can quickly be found using the Granule Coverage Map images from the AIRS Image Gallery, or directly from the discnrt1 and discnrt2 servers. Figure 2 shows an example that gives the locations of the AIRS granules used to create the images shown in Figure 1. The AIRS Image Gallery provides png images for the ascending node (when the space craft is moving northward), descending node (when the space craft is moving southward), and polar granules. The discnrt1 and discnrt2 servers also provide PDF documents showing all of the views.
AIRS Version 5 NRT products will continue to be available until the end of March 2013, at which time only the Version 6 products will be available.
Additional information on AIRS Near Real Time data is available at
Additional information on AIRS Version 6 Level 2 Standard Products is available at
Questions or comments? Email the NASA GES DISC Help Desk: email@example.com
Figure 1. These figures show a side-by -side comparison of AIRS NRT Version 5 (left panel) and Version 6 (right panel) total column CO converted to mixing ratio.
Figure 2. This is an example of a granule image map for the descending node granules (i.e., the granules obtained while the satellite was moving toward the south) on March 18, 2013, illustrating granule location by granule number.