New editions of the HITRAN molecular spectroscopic database and the high-temperature analog (HITEMP) have recently been released.1, 2 They are included in a compilation called HAWKS (HITRAN Atmospheric Workstation). HAWKS represents more fully a "matter" database. Besides an updated HITRAN high-resolution molecular database of about one million transitions, there are files of aerosol indices of refraction; UV line-by-line and cross-section parameters; supplemental files of gases such as ionic species and ozone parameters suitable for atmospheric non-local thermodynamic equilibrium conditions; extensive IR cross-sections now at different pressures and temperatures; and molecular parameters suitable for modeling high-temperature radiance. In addition there is a moderate-resolution band-model code, MODTRAN 3. There is also vastly improved software handling of the data in both WINDOW and UNIX platforms, such as more-sophisticated selection filters, plotting capabilities, pointers to significant references, and documentation.
The line-by-line portion of the compilation, HITRAN, now contains about one million transitions for some 37 molecular species. Table 1 illustrates the number of transitions, broken down by molecule. This table, however, does not reflect the fact that many species in HITRAN include significant isotopic variants, which are necessary for atmospheric simulations. One also notices that certain "heavy" molecules, such as ozone and nitric acid, have a very large number of transitions; this occurs as new bands or more-extensive coverage of bands are achieved in new editions. On the other hand, species like water vapor and carbon dioxide remain rather constant in terms of the number of transitions, even though there may be considerable improvement in the quality of the individual parameters.
The enhancements to the new compilation have been particularly focused on improving the capabilities for atmospheric remote sensing. Parameters for molecular transitions that will be needed for remote observations from space-borne missions (EOS) and ground-based measurements Atmospheric Radiation Measurement (ARM) program have been the top priority of the recent development of the compilation. Further efforts will be made to improve the parameters for weak, but nonetheless significant, transitions and bands, especially in spectral regions where there is presently a deficiency. Some of these transitions act as atmospheric interferents in the EOS experiments rather than sources. A considerable effort is now being made to include cross-sections of species at different pressure-temperature pairs. These coefficients are now being successfully incorporated into various transmission calculation schemes. Finally, aerosol indices of refraction are now being included in the compilation. It is in this area that we expect development of a standardized format that can be applied to general codes.
With regard to the major improvements in the line-by-line portion of HITRAN, in the compilation, we summarize the changes for several species in particular. For water vapor, the changes affected have been in the long-wavelength region where use of DND (Direct Numerical Diagonalization) and high-temperature experiments conducted at the Geophysics Lab have corrected or validated almost 1000 line positions. Some of the previous errors can be attributed to high-J lines, where there were previously insufficient levels for proper determination using combination differences. Carbon dioxide has been thoroughly updated using DND for the intensities of bands not measured in the laboratory; however, the changes are mostly small compared to the last edition of HITRAN. Ozone has seen a major revision: numerous new bands are now included, improvements have been made to some existing bands, and more isotopic bands have been included. Nitrous oxide (N2O) has had a major revision; carbon monoxide has been marginally improved using a subset of the parameters that have gone on the HITEMP database; oxygen has undergone a major re-calculation; nitric oxide (NO) has seen an update of the fundamental and overtone bands; nitrogen dioxide (NO2) has had a major revision; and overtone bands of SO2 have been added. Ammonia (NH3) has also had a major revision, and the nitric acid (HNO3) parameters have been extended and enhanced. Several "trace" atmospheric species have been added, bringing the total number of species in HITRAN to 35. A supplemental directory has been created to incorporate line-by-line data that either have not been fully validated (as is the case for HOBr) or differ from the mainstream HITRAN (such as the ionic species NO+).
HAWKS is available on CD-ROM. The CD-ROM is being distributed to government agencies, contractors, universities, overseas research organizations, and industry. The database is in ASCII and can be accessed by a variety of operating systems. A web page, www.HITRAN.com, has been initiated. This site contains updates to the HITRAN data, new software modifications, and other relevant information concerning the molecular spectroscopic databases.
The HITRAN molecular database has been a project with strong international cooperation during its development. Laboratories throughout the world have contributed both experimental data and theoretical calculations. The impact of the HITRAN database has recently been particularly notable in areas such as global climate modeling, ozone depletion studies, the greenhouse effect, laser propagation studies, lidar, surveillance, target discrimination, and industrial process monitoring. The database is usually used as input to either high-resolution (line-by-line) transmission codes, or indirectly in moderate-resolution, band-model codes.
The current effort has been supported by the NASA EOS program, the ARM program under the Department of Energy, and the USAF Office of Scientific Research.
Table: Statistics of Molecular Data for HITRAN/HAWKS 1996
References
1. L.S. Rothman et al., "HITRAN, edition 1996," submitted to the Journal of Quantitative Spectroscopy and Radiative Transfer.
2. L.S. Rothman et al., "HITEMP, the High-Temperature Molecular Spectroscopic Database," submitted to the Journal of Quantitative Spectroscopy and Radiative Transfer.
