Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
7
20
2007
10.5194/acp-7-5467-2007
http://www.atmos-chem-phys.net/7/5467/2007/
http://www.atmos-chem-phys.net/7/5467/2007/acp-7-5467-2007.html
http://www.atmos-chem-phys.net/7/5467/2007/acp-7-5467-2007.pdf
5467
5477
2007-10-25
Analysis of Visible/SWIR surface reflectance ratios for aerosol retrievals from satellite in Mexico City urban area
A. D. de Almeida Castanho
castanho@mit.edu
R. Prinn
V. Martins
M. Herold
C. Ichoku
L. T. Molina
Massachusetts Institute of Technology, USA
JCET, University of Maryland Baltimore County, USA
NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA
Friedrich-Schiller-University Jena, Germany
Molina Center for Energy and the Environment, USA
University of Maryland, College Park, Maryland, USA
The surface reflectance ratio between the visible (VIS) and shortwave
infrared (SWIR) radiation is an important quantity for the retrieval of the
aerosol optical depth (τ<sub><i>a</i></sub>) from the MODIS sensor data. Based on
empirically determined VIS/SWIR ratios, MODIS τ<sub><i>a</i></sub> retrieval uses
the surface reflectance in the SWIR band (2.1 µm), where the
interaction between solar radiation and the aerosol layer is small, to
predict the visible reflectances in the blue (0.47 µm) and red (0.66 µm) bands. Therefore, accurate knowledge of the VIS/SWIR ratio is
essential for achieving accurate retrieval of aerosol optical depth from
MODIS. We analyzed the surface reflectance over some distinct surface covers
in and around the Mexico City metropolitan area (MCMA) using MODIS radiances
at 0.66 µm and 2.1 µm. The analysis was performed at 1.5 km×1.5 km spatial resolution. Also, ground-based AERONET sun-photometer data
acquired in Mexico City from 2002 to 2005 were analyzed for aerosol depth and other aerosol optical properties. In addition, a network of
hand-held sun-photometers deployed in Mexico City, as part of the MCMA-2006
Study during the MILAGRO Campaign, provided an unprecedented measurement of
τ<sub><i>a</i></sub> in 5 different sites well distributed in the city. We found
that the average RED/SWIR ratio representative of the urbanized sites
analyzed is 0.73±0.06 for scattering angles <140° and goes up to
0.77±0.06 for higher ones. The average ratio for non-urban sites was
significantly lower (approximately 0.55). In fact, this ratio strongly
depends on differences in urbanization levels (i.e. relative urban to
vegetation proportions and types of surface materials). The aerosol optical
depth retrieved from MODIS radiances at a spatial resolution of 1.5 km×1.5 km
and averaged within 10×10 km boxes were compared with collocated 1-h
τ<sub><i>a</i></sub> averaged from sun-photometer measurements. The use of the new
RED/SWIR ratio of 0.73 in the MODIS retrieval over Mexico City led to a
significant improvement in the agreement between the MODIS and
sun-photometer AOD results; with the slope, offset, and the correlation
coefficient of the linear regression changing from (τ<sub><i>a</i>MODIS</sub>=0.91τ<sub><i>a</i> sun-photometer</sub>+0.33, <i>R</i><sup>2</sup>=0.66) to (τ<sub><i>a</i>MODIS</sub>=0.96 τ<sub><i>a</i> sun-photometer</sub>−0.006, <i>R</i><sup>2</sup>=0.87).
Indeed, an underestimation of this ratio in urban areas lead to a
significant overestimation of the AOD retrieved from satellite. Therefore,
we strongly encourage similar analyses in other urban areas to enhance the
development of a parameterization of the surface ratios accounting for urban
heterogeneities.
Al-Saadi, J., Szykman, J., Pierce, R. B., et al.: Improving national air quality forecasts with satellite aerosol observations, Bull. Am. Meteorol. Soc., 86(9), 1249–1264, 2005.
Castanho, A. D. A., Martins, J. V., Hobbs, P. V., Artaxo, P., Remer, L., and Yamasoe, M. A.: Chemical characterization of aerosols on the East Coast of the United States using aircraft and ground based stations during the CLAMS Experiment, J. Atmos. Sci., 62, 934–946, 2005.
Li, C., Lau, A. K. H, Mao, J., and Chu, A.: Retrieval, Validation, and Application of the 1-km Aerosol Optical Depth From MODIS Measurements Over Hong Kong, IEEE Trans. Geosci. Remote Sens, 43(11), 2650–2658, 2005.
Dubovik, O. and King, M. D.: A flexible inversion algorithm for retrieval of aerosol optical properties from sun and sky radiance measurements, J. Geophys. Res., 105(D16), 20 673–20 696, 2000.
Dubovik, O., Holben, B., Eck, T. F., Smirnov, A., Kaufman, Y. J., King, M. D., Tanré, D., and Slutsker, I.: Variability of absorption and optical properties of key aerosol types observed in worldwide locations, J. Atmos. Sci., 59, 590–608, 2002.
Gatebe, C. K., King, M. D., Tsay, S., Ji, Q., Arnold, G. T., and Li, J. Y.: Sensitivity of off-nadir zenith angles to correlation between visible and near-infrared reflectance for use in remote sensing of aerosol over land, IEEE Trans. Geosci. Remote Sens. 39(4), 805–819, 2001.
Gross, B., Ogunwuyi, O., Moshary, F., Ahmed, S.; Cairns, B.: MODIS aerosol retrieval over urban areas, Atmospheric and Environmental Remote Sensing Data Processing and Utilization: Numerical Atmospheric Prediction and Environmental Monitoring, edited by: Huang, H.-L. A., Bloom, H. J., Xu, X., and Dittberner, G., J. Proceedings of the SPIE, 5890, 274–283, 2005.
Guenther, B., Xiong, X., Salomonson, V. V., Barnes, W. L., and Young, J.: On-orbit performance of the Earth Observing System Moderate Resolution Imaging Spectroradiometer: First year of data, Remote Sens. Environ., 83, 16–30, 2002.
Herold, M., Gardner, M., and Roberts, D. A.: Spectral Resolution Requirements for Mapping Urban Areas, IEEE Transactions on Geoscience and Remote Sensing, 41(9), 1907–1919, 2003.
Holben, B. N., Tanre', D., and Smirnov, A.: An emerging ground-based aerosol climatology: Aerosol Optical depth from AERONET, J. Geophys. Res., 106(D11), 12 067–12 097, 2001.
Ichoku, C., Chu, D. A., Mattoo, S., Kaufman, Y. J., Remer, L. A., Tanré, D., Slutsker, I., and Holben, B. N.: A spatiotemporal approach for global validation and analysis of MODIS aerosol products, Geophys. Res. Lett., 29, 8006, doi:10.1029/2001GL013206, 2002a.
Ichoku, C., Levy, R., Kaufman, Y.. J., et al.: Analysis of the performance characteristics of the five-channel Microtops II sun-photometer for measuring aerosol optical thickness and precipitable water vapor, J. Geophys. Res., 107, 4179, doi:10.1029/2001JD001302, 2002b.
Kaufman, Y.J., Tanré, D., Gordon, H. R., et al.: Passive remote sensing of tropospheric aerosol and atmospheric correction for the aerosol effect, J. Geophys. Res., 102(D14), 16 815–16 830, 1997a.
Kaufman, Y.J., Tanré, D., Remer, L. A., Vermote, E. F., Chu, A., and Holben, B.: Operational remote sensing of tropospheric aerosol over land from EOS moderate resolution imaging spectroradiometer, J. Geophys. Res., 102, 17 051–17 067, 1997b.
Kaufman, Y. J., Gobron, N., Pinty, B., Widlowski, J., and Verstraete, M. M.: Relationship between surface reflectance in the visible and mid-IR used in MODIS aerosol algorithm – theory, J. Geophys. Res., 29(23), 2116, doi:10.1029/2001GL014492, 2002.
King, M. D., Menzel, W. P., Kaufman, Y.J., Tanré, D., Gao, B. C., Platnick, S., Ackerman, S. A., Remer, L. A., Pincus, R., and Hubanks, P. A.: Cloud and aerosol properties, precipitable water, and profiles of temperature and water vapor from MODIS, IEEE Trans Geosci. Remote Sens., 41(2), 442–458, 2003.
Levy, R. C., Remer, L. A., and Kaufman, Y. J.: Effects of neglecting polarization on the MODIS aerosol retrieval over land, IEEE Trans. Geosci. Rem. Sens., 42(11), 2576–2583, 2004.
Levy, R. C., Remer, L. A., Martins, J. V., and Kaufman, Y. J.: Evaluation of the MODIS aerosol retrievals over ocean and land during CLAMS experiment, J. Atmos. Sci.-Special Sect., 62, 974–992, 2005.
Levy, R. C., Remer, L. A., Matto, S., Vermote, E. F., and Kaufman, Y. J.: Second-generation operational algorithm: Retrieval of aerosol properties over land from inversion of Moderate Resolution Imaging Spectroradiometer spectral reflectance, J. Geophys. Res., 112, D13211, doi:10.1029/2006JD007811, 2007.
Martins, J. V., Tanré, D., Remer, L. A., Kaufman, Y., Mattoo, S., and Levy, R.: MODIS cloud screening for remote sensing of aerosols over ocean using spatial variability, Geophys. Res. Lett., 29(12), doi:10.1029/2001GL013252, 2002.
Meister, G.: Bidirectional Reflectance of Urban Surfaces, PhD thesis, University of Hamburg,II, Institut für Experimentalphysik, 186, URL: http://kogs-www.informatik.uni-Hamburg.de/PROJECTS/censis/publications.html, 2000.
Morys, M., Mims III, F. M., Hagerup, S., Anderson, S. E., Baker, A., Kia, J., and Walkup, T.: Design, calibration, and performance of MICROTOPS II handheld ozone monitor and sun-photometer, J. Geophys. Res., 106, 14 573–14 582, 2001.
Parkinson, C. L.: Aqua: An Earth-Observing Satellite Mission to Examine Water and Other Climate Variables, IEEE Transactions on Geoscience and Remote Sensing, 41(2), 173–183, 2003.
Remer, L. A., Wald, A. E., and Kaufman, Y.: Angular and seasonal variation of spectral surface reflectance ratios: Implications for the remote sensing of aerosol over land, IEEE Trans. Geosci. Remote Sens., 39(2), 275–283, 2001.
Remer, L.A., Kaufman, Y. J. , Tanre, D., et al.: The MODIS Aerosol Algorithm, products, and validation, J. Atmos. Sci.-Special Edition, 62, 947–973, 2005.
Ricchiazzi, P., Yang, S., Gautier, C., and Sowle, D.: SBDART: A Research and Teaching Software Tool for Plane-Parallel Radiative Transfer in the earth's Atmosphere, Bull. Am. Meteorol. Soc., 79, 2101–2114, 1998.
Roberts, D. A., Smith, M. O., and Adams, J. B.: Green Vegetation, Nonphotosynthetic Vegetation, and soils in AVIRIS Data, Remote Sensing of Environment, 44(2–3), 255–269, 1993.
Salcedo, D., Onasch, T. B., Dzepina, K., et al.: Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with Aerosol Mass Spectrometry: results from the CENICA Supersite, Atmos. Chem. Phys., 6, 925–946, 2006.
Vermote, E. F., Tanré, D, Deuze, J. L., et al.: Second Simulation of the Satellite Signal in the Solar Spectrum, 6S: An overview, IEEE Trans. Geosci. Remote Sens., 35(3), 675–686, 1997.