An instrument flown in a sustained land imaging program has a requirement to produce calibrated radiances. Calibration and validation of data products is critical for their effective use and credibility.11 A strength of the Landsat program has been the radiometric calibration of the instrument, along with spatial and temporal comparisons. The development of rigorous data products requires both onboard instrument calibration and comparison to well-known ground targets. Images without rigorous calibration support limited analyses, but the associated data will not support higher-level products. An ongoing process of instrument evaluation provides validation of radiometric data products, such as reflectances, and is a basis for validation of high-level data products. However, as quantitatively derived products, such as topography, land cover, or leaf area, are developed, these products too are based on a careful and systematic program of calibration and validation against measurements made on the ground, by aircraft underflight, and by other means. The results from these calibration/validation programs contribute to credibility and are most useful when they are openly available with the data.
Freely available data from the Landsat program have brought enormous benefits to science and to operational users.12 Higher-level products continue to be developed, providing ever greater benefits to society at large.
USGS websites and other venues effectively provide access to imagery and derived products, with varying degrees of ease of use. However, the hierarchical organization and plethora of websites and interfaces make access difficult, especially for novice users who may not know which data are on which sites.
The government currently uses a number of approaches to distribute Earth observation data: dedicated federal data centers, data federations such as the Earth Science Information Partners, commercial value-added resellers, and Internet information distributors in the private and nonprofit sectors. All these mechanisms could be used in assembling an infrastructure for the SELIP, as long as primary data and key data products remain available under an open data policy.
The potential list of baseline products and services that land imaging could provide is much larger than the suite of products and services currently provided. However, (1) the mechanisms and procedures for introducing change are cumbersome in all agencies, so the user community cannot realistically implement new products or new algorithms for existing products; (2) similar products from NASA and NOAA are global in scale and are produced whenever and wherever the input data are available, regardless of demand; and (3) the private sector supplies some derived products of varying quality and degrees of validation.
USGS, as part of the Sustained and Enhanced Land Imaging Program, should continue to deliver derived products from imagery without explicit cost to the end users.
• Improve search capabilities and transparency to users and
• Continue to interface with the private sector to improve access to public-and private-domain land imaging data products and services.
The Sustained and Enhanced Land Imaging Program should develop a systematic process for identifying and prioritizing a wider suite of products, including essential climate variables, that can be derived
11 The international Committee on Earth Observing Satellites has advocated a universal validation data set for all global land cover products to increase the interoperability of data from many countries’ satellites. It also emphasizes validation and accuracy assessments as a major part of a mapping program. Strahler et al., Global Land Cover Validation: Recommendations for Evaluation and Accuracy Assessment of Global Land Cover Maps, 2006, available at http://nofc.cfs.nrcan.gc.ca/gofc-gold/Report%20Series/GOLD_25.pdf.
12 National Geospatial Advisory Committee-Landsat Advisory Group Statement on Landsat Data Use and Charges, September 18, 2012, available at http://www.fgdc.gov/ngac/meetings/september-2012/ngac-landsat-cost-recovery-paper-FINAL.pdf.