- Email: [email protected]
Effect of the improvement of the HITRAN database on the radiative transfer calculation
ARTICLE IN PRESS
Journal of Quantitative Spectroscopy & Radiative Transfer 108 (2007) 308–318 www.elsevier.com/locate/jqsrt
Effect of the improvement of the HITRAN database on the radiative transfer calculation Xuan Fenga,b,, Feng-Sheng Zhaoa, Wen-Hua Gaoa,b a
National Satellite Meteorological Center, Beijing 100081, China Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
b
Received 7 February 2007; received in revised form 6 April 2007; accepted 20 April 2007
Abstract The line parameters of the HITRAN 2004 have been updated, as compared with the older editions (the 2000 edition and the 1996 edition). In order to know the effect of the modifications on radiative transfer calculation with high spectral resolution, comparison in optical depth and radiance spectrum have been given between different editions. Four infrared spectral regions are selected, and they cover the three bands of atmospheric infrared sounder (AIRS) and one of geosynchronous imaging fourier transform spectrometer (GIFTS). The comparison has shown that the relative difference between HITRAN 2000 and 2004 and that between HITRAN 1996 and 2004 is decreasing. But the maximal discrepancy between the latest two editions in some spectral intervals is over 1%. It is important to estimate the error of calculation with the line parameters correctly or one has to use the new edition of HITRAN. r 2007 Elsevier Ltd. All rights reserved. Keywords: The HITRAN database; Radiative transfer calculation; The line-by-line code; Spectral resolution
1. Introduction For the remote sensing of atmosphere from satellite measurements, it is essential to have a forward model that can be used to calculate the radiative transfer in the Earth–atmospheric system with a high accuracy. For example, to retrieve trace gas concentration with an accuracy of 10%, the accuracy of the forward model should be better than 1% [1]. Generally, the forward model is generated from the line-by-line code. Its accuracy is affected in many ways and the uncertainty in the spectroscopic information is one of the most important reasons. Recognized as the international standard database, the HITRAN molecular spectroscopic database has been updated several times. Its newly updated edition was released in 2004, in which the most significant improvements related to the line parameters [2]. Corresponding author. National Satellite Meteorological Center, 46 Zhongguancun Nandajie, Beijing 100081, China. Tel.: +86 10 68406124. E-mail address: [email protected] (X. Feng).
0022-4073/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jqsrt.2007.04.003
ARTICLE IN PRESS X. Feng et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 108 (2007) 308–318
309
How do modifications of the line parameters in the HITRAN database affect the radiative transfer calculations? To answer this question, we compare the line-by-line calculation results of the 2004 edition with those of 2000 (including the update through 2001) [3] and 1996 [4] editions. The infrared spectral regions that
Fig. 1. Relative differences in optical depth spectrum for the spectral range 649–1136 cm 1 between 2004 edition and (a) the 2000 edition and (b) 1996 edition. Top panel: optical depth spectrum calculated with 2004 edition; lower panels: relative differences at different spectral resolutions.
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cover the sounding bands of the atmospheric infrared sounder (AIRS) [5] and the geosynchronous imaging fourier transform spectrometer (GIFTS) [6] are selected in our calculations. 2. Outline of the line-by-line calculation The line-by-line radiation transfer model (LBLRTM) [7] is used in our radiative transfer calculations. At all pressure levels, LBLRTM uses the Voigt line shape with a line cutoff of 25 cm 1 from the line centre. The algorithmic accuracy of LBLRTM is approximately 0.5%. Such error is much less than those associated with the line parameters and the line shape, which are the limiting errors in the model [8]. The effects of the line coupling and continuum absorption are not considered in our calculations. The AIRS [5] provides infrared spectral coverage in three bands (649 1136, 1265 1629; and 2169 2674 cm 1 ) and the spectral resolution is 0:5 2:0 cm 1 . The GIFTS [6] covers the infrared spectral bands 685–1130 and 1650–2250 cm 1 with a maximum spectral resolution of 0.6 cm 1. In order to analyze the effects of improvements of the HITRAN database on the atmospheric sounding of AIRS and GIFTS, in our radiative calculations, the spectral regions cover the three bands of AIRS and one (1650–2250 cm 1) of GIFTS, and the spectral resolutions are 0.5, 1.0, and 2.0 cm 1. The tropical atmospheric profile is used in our calculations. The path length of atmosphere is from 0.0 to 50 km and the absorbers included in the calculations are H2O, CO2, O3, N2O, CO, CH4, and O2. The mixing ratio of CO2 is 380 ppmv. 3. Results Fig. 1 shows the optical depth spectrum and the associated relative difference (here, the relative difference is calculated with reference to the optical depth for the HITRAN 2004) between calculation with different editions of HITRAN for the spectral region 649–1136 cm 1. The comparison between the 1996 edition and the 2004 edition is plotted in Fig. 1b. When the spectral resolution is 0.5 cm 1, the maximum relative difference is
Fig. 2. Relative difference in optical depth spectrum for O3 between 2004 and 2000 editions. Top panel: spectral resolution is 0.5 cm lower panel spectral resolution 2.0 cm 1.
1
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41% and RMS deviation is 10%. For the resolution of 2.0 cm 1, the maximum difference is 25% and RMS deviation is 7%. Fig. 1a shows the comparison between HITRAN 2000 and 2004. The difference is less than that in Fig. 1b. But in the spectral region 980–1070 cm 1, the discrepancy is relatively large. In this
Fig. 3. Relative difference in optical depth spectrum for the spectral range 1265–1629 cm 1 between 2004 edition and (a) 2000 edition and (b) 1996 edition. Top panel: optical depth spectrum calculated with 2004 edition; lower panels: relative differences at different spectral resolutions.
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region, O3 is the main absorber and the modification of line parameters of O3 is the leading cause of this discrepancy. Fig. 2 shows the relative difference in the optical depth spectrum between HITRAN 2000 and 2004 for O3 only. It can be found that the magnitude and the contour of the relative difference spectrum are all similar to those in Fig. 1a. Fig. 3 shows the comparison in the optical depth spectrum between different editions of HITRAN for the spectral region 1265–1629 cm 1. Comparison between the calculation with HITRAN 1996 and 2004 is plotted in Fig. 3b. When the spectral resolution is 0.5 cm 1, the maximum relative difference is 30% and RMS deviation is 5%; for 2.0 cm 1, the maximum difference is 16% and RMS deviation is 3%. The difference between HITRAN 2000 and 2004 as shown in Fig. 3a is less than that in Fig. 3b. The relatively large discrepancy from 1550 to 1600 cm 1 is mainly due to the update of line parameters of H2O, and the absorption of H2O plays an important role in this region. Fig. 4 shows the relative difference between HITRAN 2000 and 2004 for only H2O. The comparison of the optical depth specta of different editions of HITRAN for the spectral region 2169–2674 cm 1 is shown in Fig. 5. The comparison between HITRAN 2000 and 2004 is plotted in Fig. 5a, and that between HITRAN 1996 and 2004 is shown in Fig. 5b. The discrepancy from 2400 to 2450 cm 1 in Fig. 5b is marked, which has decreased in Fig. 5a. But, the difference between HITRAN 2000 and 2004 is still large in some spectral regions. In Fig. 5a, when the spectral resolution is 0.5 cm 1, the maximal discrepancy is 45%; for 2.0 cm 1, the maximal discrepancy is 10%. For the spectral region 2600–2675 cm 1, the same calculation has been given to different molecules. The results, as plotted in Fig. 6, show that the absorption of H2O plays an important role in this region, and the discrepancy is mainly due to the update of line parameters of H2O. For the spectral range 1650–2250 cm 1, the comparison in the optical spectrum between HITRAN 2000 and 2004 is plotted in Fig. 7a and the comparison between HITRAN 1996 and 2004 is plotted in Fig. 7b. The discrepancy in Fig. 7b has decreased when compared with Fig. 7a. But, in Fig. 7a, the relative difference is still large in some spectral intervals, for example, in the region 1950–2050 cm 1. The same calculation is given to different molecules in this region and it is found that the difference is mainly due to the update
Fig. 4. Relative difference in optical depth spectrum for H2O between 2004 edition and the 2000 edition. Top panel: spectral resolution is 0.5 cm 1, lower panel 2.0 cm 1.
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Fig. 5. Relative difference in optical depth spectrum for the spectral range 2169–2674 cm 1 between 2004 edition and (a) the 2000 edition and (b) 1996 edition. Top panel: optical depth spectrum calculated with 2004 edition, lower panels: relative differences at different spectral resolutions.
of line parameters of H2O. Fig. 8 shows the relative difference between HITRAN 2000 and 2004 for only H2O. The upwelling radiance spectra at the top of atmosphere for different spectral regions are given in Figs. 9–12. Radiance spectrum calculated with the 2004 edition is presented in the top panel in each figure; the
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Fig. 6. Relative difference in optical depth spectrum for H2O between 2004 edition and 2000 edition. Top panel: spectral resolution is 0.5 cm 1, and in the lower panel 2.0 cm 1.
associated difference between different editions of HITRAN is shown in the lower three panels in each figure, where the spectral resolutions are 0.5, 1.0, and 2.0 cm 1, respectively. The relative difference in the radiance spectrum between calculations with HITRAN 2000 and 2004 is less than that between HITRAN 1996 and 2004. For a high spectral resolution of 0.5 cm 1, the maximal discrepancy decreases from 5% to 2% in spectral regions 649–1136 and 1265–1629 cm 1; the maximal discrepancy decreases from 3% to 1% in 2169–2674 cm 1, and the maximal discrepancy decreases from 10% to 5% especially in 1650–2250 cm 1. It is exciting to find that the relative difference between HITRAN 2000 and 2004 and that between HITRAN 1996 and 2004 is decreasing. But, for the high spectral resolution applications, the difference in some spectral intervals should be paid attention to, because, as mentioned before, an accuracy of 1% for the forward model is needed to retrieve trace gas concentrations with an accuracy of 10% [8].
4. Conclusions The line parameters of the latest edition of the HITRAN database have been modified since the previous update of 2001. In order to know the effects of the modifications, the radiative transfer calculations have been given for the spectral regions that cover the three bands of AIRS and one of GIFTS. First of all, the comparisons between different editions of the HITRAN database have shown good convergence, i.e., the relative difference between HITRAN 2000 and 2004 and that between HITRAN 1996 and 2004 is decreasing. For example, when the spectral resolution is 0.5 cm 1, the maximal discrepancy in the optical depth calculation decreases from 40% (comparison between HITRAN 1996 and 2004) to 8% (comparison between HITRAN 2000 and 2004) and the maximal discrepancy in the radiance calculation decreases from 5% (comparison between HITRAN 1996 and 2004) to 2% (comparison between HITRAN 2000 and 2004) in the spectral region 649–1136 cm 1.
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Fig. 7. Relative differences in optical depth spectrum for the spectral range 1650–2250 cm 1 between 2004 edition and (a) the 2000 edition and (b) 1996 edition. Top panel: optical depth spectrum calculated with 2004 edition; lower panels: relative differences at different spectral resolutions.
On the other hand, the maximal discrepancy between HITRAN 2000 and 2004 in some spectral intervals is still large. For example, in the region 1650–2250 cm 1, when the spectral resolution is 0.5 cm 1, the relative difference in the radiance calculation is 5%.
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Fig. 8. Relative difference in optical depth spectrum for H2O between 2004 edition and 2000 editions. Top panel: spectral resolution is 0.5 cm 1 and in the lower panel 2.0 cm 1.
Fig. 9. Relative difference in radiance spectrum for the spectral interval 649–1136 cm 1. Top panel: radiance spectrum calculated with 2004 edition and in the lower panels relative differences at different spectral resolutions are provided. The comparison between 1996 and 2004 editions is shown by dotted line.
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Fig. 10. Relative difference in radiance spectrum for the spectral interval 1265–1629 cm 1. Top panel: radiance spectrum calculated with 2004 edition and in the lower panels the relative differences at different spectral resolution are provided. The comparison between the 1996 and the 2004 editions is shown by dotted line.
Fig. 11. Relative difference in radiance spectrum for the spectral interval 2169–2674 cm 1. Top panel: radiance spectrum calculated with 2004 edition and in the lower panels the relative difference at different spectral resolution are provided. The comparison between the 1996 and the 2004 editions is shown by dotted line.
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Fig. 12. Relative difference in radiance spectrum for the spectral interval 1650–2250 cm 1. Top panel: radiance spectrum calculated with 2004 edition and in the lower panels relative difference at different spectral resolutions are provided. The comparison between 1996 and 2004 editions is shown by dotted line.
In order to improve the accuracy of atmospheric sounding, it is important to estimate the error of calculation with the line parameters correctly or to use the new edition of HITRAN. Acknowledgments The authors would like to acknowledge Mark Shephard for providing some documentation describing LBLRTM, Larry Rothman for providing a CD ROM with the HITRAN 2000 edition. References [1] Edwards DP, Francis GL. Improvements to the correlated-k radiative transfer method: application to satellite infrared sounding. J Geophys Res 2000;105:18135–56. [2] Rothman LS, Jacquemart D, Barbe A, Benner DC, Birk M, Brown LR, et al. The HITRAN 2004 Molecular Spectroscopic Database. JQSRT 2005;96:139–204. [3] Rothman LS, Barbe A, Benner DC, Brown LR, Camy-Peyret C, Carleer M, et al. The HITRAN molecualr spectroscopic database: edition of 2000 including updates through 200. JQSRT 2003;82:5–44. [4] Rothman LS, Rinsland CP, Goldman A, Massie ST, Edwards DP, Flaud J-M, et al. The HITRAN molecular spectroscopic database and HAWKS (HITRAN atmospheric workstation): 1996 edition. JQSRT 1998;60:665–710. [5] Atmospheric Infrared Sounder (AIRS) Instrument Guide, AIRS instrument guide, /http://disc.gsfc.nasa.gov/AIRS/documentation. shtmlS. [6] Smith WL, Revercomb HE, Bingham G, Huang HL, Zhou DK, Velden CS, et al. GIFTS—hyperspectral imaging and sounding from geostationary orbit. 20th international conference on interactive information and processing systems (IIPS) for meteorology, oceanography, and hydrology, 2004. [7] Clough SA, Iacono MJ, Moncet JL. Line-by-line calculation of atmospheric fluxes and cooling rates: application to water vapor. J Geophys Res 1992;97:15761–85. [8] Mlawer EJ, Taubman SJ, Brown PD, Iacono MJ, Clough SA. Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave. J Geophys Res 1997;102:16663–82.
Journal of Quantitative Spectroscopy & Radiative Transfer 108 (2007) 308–318 www.elsevier.com/locate/jqsrt
Effect of the improvement of the HITRAN database on the radiative transfer calculation Xuan Fenga,b,, Feng-Sheng Zhaoa, Wen-Hua Gaoa,b a
National Satellite Meteorological Center, Beijing 100081, China Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
b
Received 7 February 2007; received in revised form 6 April 2007; accepted 20 April 2007
Abstract The line parameters of the HITRAN 2004 have been updated, as compared with the older editions (the 2000 edition and the 1996 edition). In order to know the effect of the modifications on radiative transfer calculation with high spectral resolution, comparison in optical depth and radiance spectrum have been given between different editions. Four infrared spectral regions are selected, and they cover the three bands of atmospheric infrared sounder (AIRS) and one of geosynchronous imaging fourier transform spectrometer (GIFTS). The comparison has shown that the relative difference between HITRAN 2000 and 2004 and that between HITRAN 1996 and 2004 is decreasing. But the maximal discrepancy between the latest two editions in some spectral intervals is over 1%. It is important to estimate the error of calculation with the line parameters correctly or one has to use the new edition of HITRAN. r 2007 Elsevier Ltd. All rights reserved. Keywords: The HITRAN database; Radiative transfer calculation; The line-by-line code; Spectral resolution
1. Introduction For the remote sensing of atmosphere from satellite measurements, it is essential to have a forward model that can be used to calculate the radiative transfer in the Earth–atmospheric system with a high accuracy. For example, to retrieve trace gas concentration with an accuracy of 10%, the accuracy of the forward model should be better than 1% [1]. Generally, the forward model is generated from the line-by-line code. Its accuracy is affected in many ways and the uncertainty in the spectroscopic information is one of the most important reasons. Recognized as the international standard database, the HITRAN molecular spectroscopic database has been updated several times. Its newly updated edition was released in 2004, in which the most significant improvements related to the line parameters [2]. Corresponding author. National Satellite Meteorological Center, 46 Zhongguancun Nandajie, Beijing 100081, China. Tel.: +86 10 68406124. E-mail address: [email protected] (X. Feng).
0022-4073/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jqsrt.2007.04.003
ARTICLE IN PRESS X. Feng et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 108 (2007) 308–318
309
How do modifications of the line parameters in the HITRAN database affect the radiative transfer calculations? To answer this question, we compare the line-by-line calculation results of the 2004 edition with those of 2000 (including the update through 2001) [3] and 1996 [4] editions. The infrared spectral regions that
Fig. 1. Relative differences in optical depth spectrum for the spectral range 649–1136 cm 1 between 2004 edition and (a) the 2000 edition and (b) 1996 edition. Top panel: optical depth spectrum calculated with 2004 edition; lower panels: relative differences at different spectral resolutions.
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cover the sounding bands of the atmospheric infrared sounder (AIRS) [5] and the geosynchronous imaging fourier transform spectrometer (GIFTS) [6] are selected in our calculations. 2. Outline of the line-by-line calculation The line-by-line radiation transfer model (LBLRTM) [7] is used in our radiative transfer calculations. At all pressure levels, LBLRTM uses the Voigt line shape with a line cutoff of 25 cm 1 from the line centre. The algorithmic accuracy of LBLRTM is approximately 0.5%. Such error is much less than those associated with the line parameters and the line shape, which are the limiting errors in the model [8]. The effects of the line coupling and continuum absorption are not considered in our calculations. The AIRS [5] provides infrared spectral coverage in three bands (649 1136, 1265 1629; and 2169 2674 cm 1 ) and the spectral resolution is 0:5 2:0 cm 1 . The GIFTS [6] covers the infrared spectral bands 685–1130 and 1650–2250 cm 1 with a maximum spectral resolution of 0.6 cm 1. In order to analyze the effects of improvements of the HITRAN database on the atmospheric sounding of AIRS and GIFTS, in our radiative calculations, the spectral regions cover the three bands of AIRS and one (1650–2250 cm 1) of GIFTS, and the spectral resolutions are 0.5, 1.0, and 2.0 cm 1. The tropical atmospheric profile is used in our calculations. The path length of atmosphere is from 0.0 to 50 km and the absorbers included in the calculations are H2O, CO2, O3, N2O, CO, CH4, and O2. The mixing ratio of CO2 is 380 ppmv. 3. Results Fig. 1 shows the optical depth spectrum and the associated relative difference (here, the relative difference is calculated with reference to the optical depth for the HITRAN 2004) between calculation with different editions of HITRAN for the spectral region 649–1136 cm 1. The comparison between the 1996 edition and the 2004 edition is plotted in Fig. 1b. When the spectral resolution is 0.5 cm 1, the maximum relative difference is
Fig. 2. Relative difference in optical depth spectrum for O3 between 2004 and 2000 editions. Top panel: spectral resolution is 0.5 cm lower panel spectral resolution 2.0 cm 1.
1
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41% and RMS deviation is 10%. For the resolution of 2.0 cm 1, the maximum difference is 25% and RMS deviation is 7%. Fig. 1a shows the comparison between HITRAN 2000 and 2004. The difference is less than that in Fig. 1b. But in the spectral region 980–1070 cm 1, the discrepancy is relatively large. In this
Fig. 3. Relative difference in optical depth spectrum for the spectral range 1265–1629 cm 1 between 2004 edition and (a) 2000 edition and (b) 1996 edition. Top panel: optical depth spectrum calculated with 2004 edition; lower panels: relative differences at different spectral resolutions.
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region, O3 is the main absorber and the modification of line parameters of O3 is the leading cause of this discrepancy. Fig. 2 shows the relative difference in the optical depth spectrum between HITRAN 2000 and 2004 for O3 only. It can be found that the magnitude and the contour of the relative difference spectrum are all similar to those in Fig. 1a. Fig. 3 shows the comparison in the optical depth spectrum between different editions of HITRAN for the spectral region 1265–1629 cm 1. Comparison between the calculation with HITRAN 1996 and 2004 is plotted in Fig. 3b. When the spectral resolution is 0.5 cm 1, the maximum relative difference is 30% and RMS deviation is 5%; for 2.0 cm 1, the maximum difference is 16% and RMS deviation is 3%. The difference between HITRAN 2000 and 2004 as shown in Fig. 3a is less than that in Fig. 3b. The relatively large discrepancy from 1550 to 1600 cm 1 is mainly due to the update of line parameters of H2O, and the absorption of H2O plays an important role in this region. Fig. 4 shows the relative difference between HITRAN 2000 and 2004 for only H2O. The comparison of the optical depth specta of different editions of HITRAN for the spectral region 2169–2674 cm 1 is shown in Fig. 5. The comparison between HITRAN 2000 and 2004 is plotted in Fig. 5a, and that between HITRAN 1996 and 2004 is shown in Fig. 5b. The discrepancy from 2400 to 2450 cm 1 in Fig. 5b is marked, which has decreased in Fig. 5a. But, the difference between HITRAN 2000 and 2004 is still large in some spectral regions. In Fig. 5a, when the spectral resolution is 0.5 cm 1, the maximal discrepancy is 45%; for 2.0 cm 1, the maximal discrepancy is 10%. For the spectral region 2600–2675 cm 1, the same calculation has been given to different molecules. The results, as plotted in Fig. 6, show that the absorption of H2O plays an important role in this region, and the discrepancy is mainly due to the update of line parameters of H2O. For the spectral range 1650–2250 cm 1, the comparison in the optical spectrum between HITRAN 2000 and 2004 is plotted in Fig. 7a and the comparison between HITRAN 1996 and 2004 is plotted in Fig. 7b. The discrepancy in Fig. 7b has decreased when compared with Fig. 7a. But, in Fig. 7a, the relative difference is still large in some spectral intervals, for example, in the region 1950–2050 cm 1. The same calculation is given to different molecules in this region and it is found that the difference is mainly due to the update
Fig. 4. Relative difference in optical depth spectrum for H2O between 2004 edition and the 2000 edition. Top panel: spectral resolution is 0.5 cm 1, lower panel 2.0 cm 1.
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Fig. 5. Relative difference in optical depth spectrum for the spectral range 2169–2674 cm 1 between 2004 edition and (a) the 2000 edition and (b) 1996 edition. Top panel: optical depth spectrum calculated with 2004 edition, lower panels: relative differences at different spectral resolutions.
of line parameters of H2O. Fig. 8 shows the relative difference between HITRAN 2000 and 2004 for only H2O. The upwelling radiance spectra at the top of atmosphere for different spectral regions are given in Figs. 9–12. Radiance spectrum calculated with the 2004 edition is presented in the top panel in each figure; the
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Fig. 6. Relative difference in optical depth spectrum for H2O between 2004 edition and 2000 edition. Top panel: spectral resolution is 0.5 cm 1, and in the lower panel 2.0 cm 1.
associated difference between different editions of HITRAN is shown in the lower three panels in each figure, where the spectral resolutions are 0.5, 1.0, and 2.0 cm 1, respectively. The relative difference in the radiance spectrum between calculations with HITRAN 2000 and 2004 is less than that between HITRAN 1996 and 2004. For a high spectral resolution of 0.5 cm 1, the maximal discrepancy decreases from 5% to 2% in spectral regions 649–1136 and 1265–1629 cm 1; the maximal discrepancy decreases from 3% to 1% in 2169–2674 cm 1, and the maximal discrepancy decreases from 10% to 5% especially in 1650–2250 cm 1. It is exciting to find that the relative difference between HITRAN 2000 and 2004 and that between HITRAN 1996 and 2004 is decreasing. But, for the high spectral resolution applications, the difference in some spectral intervals should be paid attention to, because, as mentioned before, an accuracy of 1% for the forward model is needed to retrieve trace gas concentrations with an accuracy of 10% [8].
4. Conclusions The line parameters of the latest edition of the HITRAN database have been modified since the previous update of 2001. In order to know the effects of the modifications, the radiative transfer calculations have been given for the spectral regions that cover the three bands of AIRS and one of GIFTS. First of all, the comparisons between different editions of the HITRAN database have shown good convergence, i.e., the relative difference between HITRAN 2000 and 2004 and that between HITRAN 1996 and 2004 is decreasing. For example, when the spectral resolution is 0.5 cm 1, the maximal discrepancy in the optical depth calculation decreases from 40% (comparison between HITRAN 1996 and 2004) to 8% (comparison between HITRAN 2000 and 2004) and the maximal discrepancy in the radiance calculation decreases from 5% (comparison between HITRAN 1996 and 2004) to 2% (comparison between HITRAN 2000 and 2004) in the spectral region 649–1136 cm 1.
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Fig. 7. Relative differences in optical depth spectrum for the spectral range 1650–2250 cm 1 between 2004 edition and (a) the 2000 edition and (b) 1996 edition. Top panel: optical depth spectrum calculated with 2004 edition; lower panels: relative differences at different spectral resolutions.
On the other hand, the maximal discrepancy between HITRAN 2000 and 2004 in some spectral intervals is still large. For example, in the region 1650–2250 cm 1, when the spectral resolution is 0.5 cm 1, the relative difference in the radiance calculation is 5%.
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Fig. 8. Relative difference in optical depth spectrum for H2O between 2004 edition and 2000 editions. Top panel: spectral resolution is 0.5 cm 1 and in the lower panel 2.0 cm 1.
Fig. 9. Relative difference in radiance spectrum for the spectral interval 649–1136 cm 1. Top panel: radiance spectrum calculated with 2004 edition and in the lower panels relative differences at different spectral resolutions are provided. The comparison between 1996 and 2004 editions is shown by dotted line.
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Fig. 10. Relative difference in radiance spectrum for the spectral interval 1265–1629 cm 1. Top panel: radiance spectrum calculated with 2004 edition and in the lower panels the relative differences at different spectral resolution are provided. The comparison between the 1996 and the 2004 editions is shown by dotted line.
Fig. 11. Relative difference in radiance spectrum for the spectral interval 2169–2674 cm 1. Top panel: radiance spectrum calculated with 2004 edition and in the lower panels the relative difference at different spectral resolution are provided. The comparison between the 1996 and the 2004 editions is shown by dotted line.
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Fig. 12. Relative difference in radiance spectrum for the spectral interval 1650–2250 cm 1. Top panel: radiance spectrum calculated with 2004 edition and in the lower panels relative difference at different spectral resolutions are provided. The comparison between 1996 and 2004 editions is shown by dotted line.
In order to improve the accuracy of atmospheric sounding, it is important to estimate the error of calculation with the line parameters correctly or to use the new edition of HITRAN. Acknowledgments The authors would like to acknowledge Mark Shephard for providing some documentation describing LBLRTM, Larry Rothman for providing a CD ROM with the HITRAN 2000 edition. References [1] Edwards DP, Francis GL. Improvements to the correlated-k radiative transfer method: application to satellite infrared sounding. J Geophys Res 2000;105:18135–56. [2] Rothman LS, Jacquemart D, Barbe A, Benner DC, Birk M, Brown LR, et al. The HITRAN 2004 Molecular Spectroscopic Database. JQSRT 2005;96:139–204. [3] Rothman LS, Barbe A, Benner DC, Brown LR, Camy-Peyret C, Carleer M, et al. The HITRAN molecualr spectroscopic database: edition of 2000 including updates through 200. JQSRT 2003;82:5–44. [4] Rothman LS, Rinsland CP, Goldman A, Massie ST, Edwards DP, Flaud J-M, et al. The HITRAN molecular spectroscopic database and HAWKS (HITRAN atmospheric workstation): 1996 edition. JQSRT 1998;60:665–710. [5] Atmospheric Infrared Sounder (AIRS) Instrument Guide, AIRS instrument guide, /http://disc.gsfc.nasa.gov/AIRS/documentation. shtmlS. [6] Smith WL, Revercomb HE, Bingham G, Huang HL, Zhou DK, Velden CS, et al. GIFTS—hyperspectral imaging and sounding from geostationary orbit. 20th international conference on interactive information and processing systems (IIPS) for meteorology, oceanography, and hydrology, 2004. [7] Clough SA, Iacono MJ, Moncet JL. Line-by-line calculation of atmospheric fluxes and cooling rates: application to water vapor. J Geophys Res 1992;97:15761–85. [8] Mlawer EJ, Taubman SJ, Brown PD, Iacono MJ, Clough SA. Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave. J Geophys Res 1997;102:16663–82.