Search Results
You are looking at 1 - 2 of 2 items for
- Author or Editor: Aleksandr M. Ignatov x
- Refine by Access: All Content x
Abstract
Recently, a statistical procedure was proposed to analyze the angular effect in the NOAA Advanced Very High Resolution Radiometer (AVHRR) brightness temperatures. The estimated empirical angular functions (EAF) over the oceans allow one to check the algorithms for the sea surface temperature (SST) and the column water vapor content when the observation geometry is variable, as well as to test angular methods of SST retrieval. The EAF approach has been previously applied to the analysis of the AVHRR brightness temperatures in channels 3 and 4 and dual-window SST over the tropical Atlantic in June 1987 and December 1988 from NOAA-10 and NOAA-11, respectively. Here, it is extended to estimate the accuracy of the split-window sea surface temperature and atmospheric water vapor retrievals from NOAA-9 over the tropical and North Atlantic in July 1986. The authors confirm the previously drawn conclusion that in a general case no angle-independent coefficients in a linear SST retrieval algorithm can provide angle-invariant retrievals. More recent operational NOAA angle-dependent algorithms have been shown to improve retrievals in the Tropics. In high latitudes, they seem to slightly overcorrect the angular effect. Using satellite data of higher spatial resolution with better radiometric accuracy is expected to improve the accuracy of the EAFs and the reliability of the conclusions.
Abstract
Recently, a statistical procedure was proposed to analyze the angular effect in the NOAA Advanced Very High Resolution Radiometer (AVHRR) brightness temperatures. The estimated empirical angular functions (EAF) over the oceans allow one to check the algorithms for the sea surface temperature (SST) and the column water vapor content when the observation geometry is variable, as well as to test angular methods of SST retrieval. The EAF approach has been previously applied to the analysis of the AVHRR brightness temperatures in channels 3 and 4 and dual-window SST over the tropical Atlantic in June 1987 and December 1988 from NOAA-10 and NOAA-11, respectively. Here, it is extended to estimate the accuracy of the split-window sea surface temperature and atmospheric water vapor retrievals from NOAA-9 over the tropical and North Atlantic in July 1986. The authors confirm the previously drawn conclusion that in a general case no angle-independent coefficients in a linear SST retrieval algorithm can provide angle-invariant retrievals. More recent operational NOAA angle-dependent algorithms have been shown to improve retrievals in the Tropics. In high latitudes, they seem to slightly overcorrect the angular effect. Using satellite data of higher spatial resolution with better radiometric accuracy is expected to improve the accuracy of the EAFs and the reliability of the conclusions.
Abstract
This paper deals with the problem of aerosol optical thickness (τ A ) retrieval using sun-photometer measurements. The results of the theoretical analysis and computer processing of the dataset collected during the 40th cruise of the R/V Akademik Vernadsky are presented. Accuracy of retrieved τ A is investigated in detail. It is concluded that 1) the τ A measurements from the three shortest wavelength channels are sufficiently accurate (0.02–0.03) for evaluation of the NOAA Advanced Very High Resolution Radiometer aerosol optical thickness operational product; 2) serious discrepancies exist between observation and theory for the two longest wavelength channels, which preclude their use in aerosol optical property studies. Further investigations are required, with emphasis on the computation of atmospheric gaseous absorption, before these channels can be used. Shipboard τ A will be compared with satellite data from the NOAA/National Environment Satellite Data and Information Service in a subsequent paper.
Abstract
This paper deals with the problem of aerosol optical thickness (τ A ) retrieval using sun-photometer measurements. The results of the theoretical analysis and computer processing of the dataset collected during the 40th cruise of the R/V Akademik Vernadsky are presented. Accuracy of retrieved τ A is investigated in detail. It is concluded that 1) the τ A measurements from the three shortest wavelength channels are sufficiently accurate (0.02–0.03) for evaluation of the NOAA Advanced Very High Resolution Radiometer aerosol optical thickness operational product; 2) serious discrepancies exist between observation and theory for the two longest wavelength channels, which preclude their use in aerosol optical property studies. Further investigations are required, with emphasis on the computation of atmospheric gaseous absorption, before these channels can be used. Shipboard τ A will be compared with satellite data from the NOAA/National Environment Satellite Data and Information Service in a subsequent paper.
