TL2HCNNS_8 is the Tropospheric Emission Spectrometer (TES)/Aura Level 2 Hydrogen Cyanide Nadir Special Observation Version 8 data product. TES Level 2 data contain retrieved species (or temperature) profiles at the observation targets and the estimated errors. The geolocation, quality, and other data (e.g., surface characteristics for nadir observations) are also provided. L2 modeled spectra are evaluated using radiative transfer modeling algorithms. The process, referred to as retrieval, compares observed spectra to the modeled spectra and iteratively updates the atmospheric parameters. L2 standard product files include information for one molecular species (or temperature) for an entire global survey or special observation run. A global survey consists of a maximum of 16 consecutive orbits.
A Nadir sequence within the TES Global Survey is a fixed number of observations within an orbit for a Global Survey. Prior to April 24, 2005, it consisted of two low resolution scans over the same ground locations. After April 24, 2005, Global Survey data consisted of three low resolution scans. The Nadir standard product consists of four files, where each file is composed of the Global Survey Nadir observations from one of four focal planes for a single orbit, i.e. 72 orbit sequences. The Global Survey Nadir observations currently only use a single set of filter mix.
A Global Survey consists of observations along 16 consecutive orbits at the start of a two day cycle, over which 3,200 retrievals are performed. Each observation is the input for retrievals of species Volume Mixing Ratios (VMR), temperature profiles, surface temperature and other data parameters with associated pressure levels, precision, total error, vertical resolution, total column density and other diagnostic quantities. Each TES Level 2 standard product reports information in a swath format conforming to the HDF-EOS Aura File Format Guidelines. Each Swath object is bounded by the number of observations in a global survey and a predefined set of pressure levels representing slices through the atmosphere. Each standard product can have a variable number of observations depending upon the Global Survey configuration and whether averaging is employed. Also, missing or bad retrievals are not reported.
The organization of data within the Swath object is based on a superset of the UARS pressure levels used to report concentrations of trace atmospheric gases. The reporting grid is the same pressure grid used for modeling. There are 67 reporting levels from 1211.53 hPa, which allows for very high surface pressure conditions, to 0.1 hPa, about 65 km. In addition, the products will report values directly at the surface when possible or at the observed cloud top level. Thus in the Standard Product files each observation can potentially contain estimates for the concentration of a particular molecule at 67 different pressure levels within the atmosphere. However, for most retrieved profiles, the highest pressure levels are not observed due to a surface at lower pressure or cloud obscuration. For pressure levels corresponding to altitudes below the cloud top or surface, where measurements were not possible, a fill value will be applied.
To minimize the duplication of information between the individual species standard products, data fields common to each species (such as spacecraft coordinates, emissivities, and other data fields) have been collected into a separate standard product, termed the TES L2 Ancillary Data product (ESDT short name: TL2ANC). Users of this product should also obtain the Ancillary Data product.