The AVHRR Polar Pathfinder Twice-Daily 25 km EASE-Grid Composites are a collection of products for both poles, consisting of twice-daily gridded and calibrated satellite channel data and derived parameters. Data include five Advanced Very High Resolution Radiometer (AVHRR) channels, clear sky surface broadband albedo and skin temperature, average albedo and temperature, valid fraction file, solar ... zenith angle, satellite elevation angle, sun-satellite relative azimuth angle, surface type mask, cloud mask, cloud fraction files, and Universal Coordinated Time (UTC) of acquisition. The 25-km data are derived from the AVHRR Polar Pathfinder Twice-Daily 5 km EASE-Grid Composites, and extend poleward from 48.4 degrees north and 53.2 degrees south latitudes, spanning July 1981 through December 2000. Data are in 1-byte and 2-byte integer grid format and are available by FTP. Note: NSIDC reccommends the use of the Extended AVHRR Polar Pathfinder (APP-x) Product, located at http://stratus.ssec.wisc.edu/products/appx/appx.html, instead of our AVHRR Polar Pathfinder Twice-Daily 25 km EASE-Grid Composites. The APP-x 25 km product has albedo and temperature calculations for all sky conditions. Cloud properties are modeled to estimate the albedo and temperature under the clouds. An improved cloud detection algorithm is also used in the APP-x product.
Channel data are accurate to within approximately +/- 0.2 percent based on sensor noise level of 0.4 data number (DN). Temperatures are accurate to within approximately 2 degrees Kelvin. Relative albedos in adjacent grid cells are accurate to within approximately 5 percent. However, absolute albedo values are approximate. Accuracies for the products are difficult to determine, given the limited ... nature of existing case studies. Also, conditions vary substantially across the large product domains and over time. Plans are being developed to further define product accuracies for snow-covered areas, sea ice, and ice sheets. Based on studies to date, accuracies in general are approximately +/- 2 degrees Kelvin for AVHRR-derived skin temperatures and +/- 0.05 degrees for surface albedo. Much of this error is likely due to uncertainties in the performance of the cloud detection methods. For clear sky conditions, accuracies for albedo and temperature products are expected to be in the range noted in the Barrow test, with temperatures accurate to +/- 0.5 degrees Celsius. Data and related information will be updated as appropriate. Additional comparisons with in-situ measurements of albedo and temperature are planned. See also Maslanik et al. (2000) for other accuracy discussions relative to SHEBA data.
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
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Ahmad, S. P., P. F. Levelt, P. K. Bhartia, E. Hilsenrath, G. W. Leppelmeier, and J. E. Johnson, Atmospheric Products from the Ozone Monitoring Instrument (OMI), Proceedings of SPIE conference on Earth Observing Systems VIII, San Diego, California, Aug 3-8, 2003. http://disc.sci.gsfc.nasa.gov/acdisc/ozone/docs/omi-spie-2003.doc
J. Joiner and A.P. Vasilkov, First Results From the OMI Rotational Raman Scattering Cloud Pressure Algorithm, IEEE Trans. Geo. Rem. Sens., 2006, Vol. 44, No. 5, 1272-1282, doi:10.1109/TGRS.2005.861385
Joiner, J., A. Vasilkov, D. Flittner, J. Gleason and P. K. Bhartia, Retrieval of Cloud Pressure and Oceanic Chlorophyll Content using Raman Scattering in GOME ultraviolet spectra, J. Geophys. Res, vol 109, doi: 10,1029/2003JD003915,2004.
Joiner, J., A. Vasilkov, D. Flittner, E. Buscela, and J. Gleason, Retrieval of Cloud Pressure from Rotational Raman Scattering, in Algorithm Theoretical Baseline Document: Clouds, Aerosols, and Surface UV Irradiance, P. Stammes (ed.), vol. III, ATBD-OMI-03, version 2.0, Aug. 2002. http://eospso.gsfc.nasa.gov/sites/default/files/atbd/ATBD-OMI-02.pdf
Joiner, J., P.K.Bhartia,R.P.Cebula, E. Hilsenrath, R.D. McPeters and H. Park,& Rotational Raman Scattering (Ring Effect) in satellite backscatter ultraviolet measurements,Appl. Opt, vol 34, pp. 4513-4525, 1995.
Joiner, J. and P.K. Bhartia, &The Determination of Cloud Pressure from Rotational Raman Scattering in Satellite Back Scatter Ultraviolet Measurements, J. Geophys. Res, vol 100, pp 23019-23026, 1995.
Levelt, P. F., B. van den Oord, E. Hilsenrath, G. W. Leppelmeier, P. K. Bhartia, A. Malkki, H. Kelder, R. J. van der A, E. J. Brinksma, R. van Oss, P. Veefkind, M. van Weele, and R. Noordhoek, &Science Objectives of EOS-Aura's Ozone Monitoring Instrument (OMI)&, Proc. Quad. Ozone Symposium, Sapporo, Japan, pp. 127-128, 2000.
Schoeberl, M.R., A.R. Douglass, E. Hilsenrath, P.K. Bhartia, J. Barnett, J. Gille, R. Beer, M. Gunson, J. Waters, P.F. Levelt, P. DeCola, &The EOS Aura Mission,& EOS, Transactions, American Geophysical Union 85 , Number 18, 4 May 2004. [ Preprint] http://aura.gsfc.nasa.gov/project/eos-agu-aura-article.pdf
Vasilkov, A. P., J. Joiner, K. Yang, R. Spurr, and P.K. Bhartia,Comparisons of OMI Cloud Pressures Derived from Rotational Raman Scattering with Collocated EOS Aqua/MODIS data with Supporting Radiative Transfer Calculations&,Validation of OMI cloud pressure, Aura Meeting, 2004. http://code916.gsfc.nasa.gov/People/Joiner/OMCLDRR_validation_web.htm
Vasilkov, A. P., J. Joiner, K. Yang, and P. K. Bhartia, &Improving total column ozone retrievals by using cloud pressures derived from RAman Scattering in the UV,& Geophys. Res. Lett. 31, L20109, doi: 10.1029/2004GL020603, 2004.