Data Validation States
Many quantities from the AIRS-team retrieval have been extensively tested and validated against other observations. The CLIMCAPS retrieval system is just beginning to be applied to the AIRS radiances, so its characteristics are not yet as well documented as the AIRS-team record. The validation states for Level 2 Data Products in the AIRS-team Version 7 release products, are given in the table below along with uncertainty estimates and vertical coverage, where applicable. A separate table gives the validation states and uncertainties for Level 1B products. These tables are only intended to give a general idea about the products. For more details on AIRS-team Version 7 Level 2 data validation, uncertainties and coverage, we refer to the product-specific sections of the AIRS V7 Level 2 Product User Guide and references therein to validation reports and relevant journal papers. The AIRS webpage also has a frequently updated searchable database for AIRS-related publications. For a detailed discussion of measurement uncertainties of AIRS L1B radiances, please see Pagano et al. (2020).
AIRS product validation states have traditionally been categorized as “Provisional” and “Validated: Stages 1-3”. The state of product validation depends upon surface type, latitude and product type.
- Prov = Provisional: Product quality is sufficient for use by the general research community, but users are urged to contact the AIRS science team before using the data in publications
- Val1 = Stage 1 Validation: Product accuracy has been estimated using a small number of independent measurements obtained from selected locations and time periods and ground-truth/field program efforts.
- Val2 = Stage 2 Validation: Product accuracy has been assessed over a widely distributed set of locations and time periods via several ground-truth and validation efforts.
- Val3 = Stage 3 Validation: Product accuracy has been assessed and the uncertainties in the product well established via independent measurements in a systematic and statistically robust way representing global conditions.
Note: The validation state for the Level 3 Gridded Data Product matches that of the corresponding Level 1B or Level 2 Data Product from which it is generated.
About the uncertainties
Uncertainties are of two types. Those with units (like temperature or cloud top pressure) give the likely range of the retrieved quantity. For example, a large number of AIRS retrieved cloud top heights of 5 km indicates clouds between 4 and 6 km 70% of the time, with a most likely height of 5 km.
Percent errors indicate the range with the retrieval value, plus or minus the fractional range. For example, a set of total water vapor retrievals of 10 kg / m^2 would range between 8 and 12 kg / m^2 about 70% of the time.
Fractional uncertainties are used for quantities which can have a large range of values, such as total water vapor which can vary between 1 kg / m^2 and 70 kg / m^2, or cloud fraction which in AIRS retrievals can vary between 0.05 and 1.0.