Multichannel Sea Surface Temperature Research Articles

Operational value-adding to AVHRR data over Europe: methods, results, and prospects

The German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) has been operating a ground segment for High Resolution Picture Transmission (HRPT) data acquisition, archiving, and distribution since the early 1980s. The station's visibility covers all of Europe. DFD started with the generation of thematic level-3 AVHRR value-added products consisting of Multichannel Sea Surface Temperatures (MCSST) and Normalized Difference Vegetation Indices (NDVI) in March 1993 [8]. Additionally, calibrated and registered 5-channel image subsets in two areas have been generated for supporting user-specific applications since 1994 [8]. The status of the current level-3 product generation chain as well as corresponding processing algorithms are presented. Perspectives are introduced to improve the existing products in terms of channel 1 and 2 radiometric optimization by implementing an atmospheric correction scheme, as well as to correct the solar channels for anisotropic reflectance with respect to different surfaces. As AVHRR data proved to be one of the major sources to derive global information on different land-oriented parameters, special emphasis is given in this paper on methods to extract land cover, the fraction of Absorbed Photosynthetic Active Radiation (fAPAR), and Leaf Area Index (LAI) with respect to operational use. Furthermore, different algorithms were discussed to derive Land Surface Temperatures (LST) by estimating surface emissivity based on NDVI time synthesis. First results over Germany are shown, problems addressed, and outlines for operational usage are given.

A comparison of satellite MCSST with ship measured SST in the North Indian Ocean

The evaluation of Multichannel Sea Surface Temperature (MCSST) weekly charts on a global scale produced by NOAA‐NESDIS has been carried out for the North Indian Ocean. It is believed that the atmospheric conditions over the North Indian Ocean affect the estimation of Sea Surface Temperature (SST) from remotely sensed data. Hence, an attempt has been made to validate the MCSSTs with the ship observations over the North Indian Ocean. The ship observations (Total 5,350) reported in the Indian Daily Weather Reports (IDWRs) were used for comparison with the MCSSTs with an assumption that the SST will not vary much during a week (< 0.5°C) in the North Indian Ocean. The total data set has been divided into seasonal (premonsoon, monsoon and post monsoon), time of the day (0000 0600 1200 and 1800 GMT) and regions (Arabian Sea, Bay of Bengal, Lower, Middle and Upper latitudes) to study the accuracies in estimation of MCSSTs over the North Indian Ocean. This division of the data set is made since the atmospheric water vapour content is highly variable over seasons, time of day and also different geographical regions. The results revealed that the accuracies of MCSSTs are better than 1°C (RMS deviation is ± 0.7) over the North Indian Ocean. It is concluded that the split window technique provides a good estimation of SSTs even in the regions where the atmospheric water vapour content is highly variable.

Centroid Motion of the Western Pacific Warm Pool during Three Recent El Niño–Southern Oscillation Events

Abstract The centroid motion of the Western Pacific warm pool for 1982–83, 1986–87 and 1991–93 El Nino–Southern Oscillation events was investigated by analyzing satellite multichannel sea surface temperature and satellite pathfinder sea surface temperature data in conjunction with wind data from The Florida State University. The authors found that the direction of motion of the warm pool’s center changes shortly before the onset of a new El Nino event and that this change was quite different during the 1991–93 El Nino than during the 1982–83 and 1986–87 El Nino events. The possible cause of these changes and differences may be the El Nino–related wind pattern shifts in the western equatorial Pacific Ocean before and during the events, and the seasonal phase-lock of the El Nino events.

Satellite derived sea surface temperature variability in the Western Tropical Pacific Ocean, 1992–1993

One year of NOAA Advanced Very High Resolution Radiometer (AVHRR) global area coverage (GAC) infrared satellite data from September 1992 to August 1993 were processed into 10-day composite sea surface temperature (SST) maps, which show the variability of SST in the Western Tropical Pacific Ocean (including the TOGA COARE area). In situ SST measurements from moored buoy data were used to validate the satellite SST products revealing the multichannel SST (MCSST) to be most representative of the buoy SSTs. An empirical orthogonal function (EOF) analysis was performed to characterize the principal components of the annual SST variability. The first EOF mode (64.2% of the variance) indicates that the variance of the satellite derived MCSST has a strong meridional structure with a marked seasonal modulation. This first mode suggests the importance of “warm pool” with a maximum just south of the equator at about 170°E. The second mode (8.7% of the variance) and the rest of the EOF modes show more complex spatial structures. The large amount of variance explained by the first mode compared to the second mode indicates that the seasonal variance of the warm pool dominates all other variability. This strong seasonal behavior is also clearly seen in the monthly meridional position of the Intertropical Convergence Zone (ITCZ). The annual mean SST map shows a persistent warm pool from 13° S to 10° N and 130° E to 170° W, which is larger than the COARE intensive observing period (IOP) domain. Monthly SST means in the region suggest a seasonal cycle in phase with the solar cycle. Warm pool total area variance and its centroid movement demonstrate similar annual cycles.

Highers—The AVHRR-based higher spatial resolution sea surface temperature data set intended for studying the ocean south of Japan

For the study of the ocean south of Japan, the HIGHER spatial resolution Sea surface temperature (HIGHERS) data have been produced from the AVHRR/NOAA data. The grid size is 0.075 degree and is much smaller than that of the usual sea surface temperature (SST) analysis field, which is gridded at most in 1 degree. In order to calculate accurate SST, the split-window Multi-Channel SST method is applied to cloudless pixels, which are detected with a cloud detection algorithm. The accuracy of the HIGHERS data is checked in comparison with the in-situ observation data.

A new method to determine near‐sea surface air temperature by using satellite data

We present a new algorithm with which to determine near‐sea surface air temperature from satellite observations. A relationship between air temperature, sea surface temperature (SST), wind speed, and humidity is obtained from the aerodynamical equation and the bulk formula. We solve air temperature from this relationship by giving other variables with the observations and without explicit assumption of boundary layer parameters. Our new method is validated using observed monthly mean data at the Japan Meteorological Agency (JMA) and Tropical Ocean‐Global Atmosphere (TOGA)‐Tropical Atmosphere Ocean (TAO) buoys. Air temperature and sensible heat flux can be determined with accuracies of 0.0° ± 1.2°C and 0.1 ± 8.7 W/m2, respectively, when SST, wind speed, and humidity are given by in situ observations. In order to retrieve near‐sea surface air temperature and sensible heat flux from satellite data, SST is obtained from multi channel sea surface temperature (MCSST) of advanced very high resolution radiometer (AVHRR), wind speed is obtained from special sensor microwave/imager (SSM/I), and humidity is obtained from SSM/I together with the empirical equation proposed by Liu [1986]. An error of monthly mean satellite‐derived air temperature is −0.3° ± 3.1°C, and that of sensible heat flux is 10.0 ± 37.6 W/m2. Errors of both satellite‐derived values are enlarged, possibly because the satellite observations have seasonably systematic error. Time evolution of the interannual variation of air temperature estimated by satellite agrees well with that of in situ measurements. The estimation error of the interannual variation of air temperature is 0.0° ± 1.5°C, and that of sensible heat flux is 0.3 ± 19.0 W/m2. At an interannual timescale the satellite‐derived sensible heat flux catches the time evolution of the in situ observation. Both the air temperature and the sensible heat flux obtained by using our method have fewer errors than estimations made by assuming relative humidity as the climatological mean value.

Phytoplankton pigment distribution and frontal structure in the subtropical convergence region south of Africa

Satellite data from the Coastal Zone Colour Scanner (CZCS) and Advanced Very High Resolution Radiometer were examined to determine the relationship between the phytoplankton pigment distribution and sea surface temperature (SST) in the Subtropical Convergence (STC) region south of Africa. The structure of the temperature fronts and their role in phytoplankton pigment distribution was explored. The multichannel sea surface temperature (MCSST) data for 1981–1986 showed considerable interannual variability in both the position of the Agulhas retroflection and the extent of the Rossby wave in the Agulhas Return Current. Pronounced interannual variation in pigment levels was found in the CZCS data for early 1979, 1982 and 1983, with highest pigment levels in early 1982. These greater pigment levels were shown to be a function of increased frontal intensity of the STC front rather than of the Agulhas front, or of SST per se. The principal interannual differences were found in the region where a strong Agulhas front occurred to the north of the STC front. The Agulhas front appeared to play a role in limiting the spatial distribution of phytoplankton pigment. Time series of level-2 CZCS data supported the scenario of upstream Agulhas retroflection resulting in a pronounced Rossby wave in the Agulhas Return Current, and increased phytoplankton pigment levels in the STC region.

A new set of MCSST equations for NOAA-9/AVHRR

A new set of multi-channel sea surface temperature (MCSST) equations for the Advanced Very High Resolution Radiometer (AVHRR) on NOAA-9 is derived from regression analyses between two-channel brightness temperatures andin situ SST obtained from moored buoys around Japan. Two equations are derived: one for daytime and the other for nighttime. They are linear split window type and both the equations contain a term dependent on satellite zenith angle, which has not been accounted for in the previous daytime split window equations for NOAA-9. It is shown that the new set of equation can give SSTs in much better precision than those without the zenith-angle-dependent terms. It is also found that the split window equation for NOAA-9 provided by the National Oceanographic and Atmospheric Administration/National Environmental Satellite, Data and Information Service (NOAA/NESDIS) considerably underestimates the daytime SSTs; sometimes nighttime SSTs are evenhigher than daytime SSTs. This is because the zenith angle effect to the radiation deficiet is neglected in the daytime equation by NOAA/NESDIS. By using the new MCSST equations, it is expected that the quality of satellite MCSST would be much improved, at least in regional applications around Japan, for the period of NOAA-9's operation.

Satellite Thermal Remote Sensing in the BITEX'93 Area

We analyzed NOAA-AVHRR temperature data from Lake Biwa. These data are low in spatial resolusion but the observations are quite frequent. Ten sets of data during the BITEX'93 period showed that the MCSST (multichannel sea surface temperature) method for data correction is also applicable to Lake Biwa. They also showed that NOAA-AVHRR data is useful to distinguish day-to-day variation of surface temperature for Lake Biwa. However, we could not find any significant and systematic spatial temperature distribution on the lake.

Maltese Front variability from satellite observations based on automated detection

Maltese Front location statistics are obtained from multichannel sea-surface temperature (MCSST) images, derived from Advanced Very High Resolution Radiometer (AVHRR) observations of the Mediterranean Sea during March 3 through September 27, 1993. The statistics are based on semiautomated determinations of the Front's sea-surface temperature surface expression. Expert analyses from the Naval Oceanographic Office give an accuracy check. Expert techniques are largely manual, labor-intensive, subjective, and skill-dependent; therefore, automation could be beneficial. A mathematical morphology-based method successfully delineates the Front. It finds the temperature gradients most likely to be the Front's and presents the corresponding segmentations to the operator. The method was developed to find stars in astronomical images, and has successfully analyzed solar magnetograms and satellite Gulf Stream images. Rings, fronts, and sunspots are not star-like, but simple preprocessing adapts the technique to these problem domains. This work constitutes another successful application. The success in "moving" the technique is encouraging. The Maltese Front's thermal gradients are 5-10 times weaker than the Gulf Stream North Wall's, yet the method produces useful results, and it may work in other regions.

Applying MCSST to coral reef bleaching

In the 1980s and early 1990s, coral reef bleaching events of unprecedented frequency and global extent were observed. Elevated water temperature is suspected as the primary causal stress of mass bleaching events from this period. The relationship between sea surface temperatures (SSTs) and coral bleaching events was investigated using National Oceanic and Atmospheric Administration (NOAA) Multi-Channel Sea Surface Temperature (MCSST) satellite imagery from 1982–1992. Nighttime MCSST weekly averages were compared with moored-buoy temperatures for sea-truthing the satellite. Average errors from 11 individual buoy comparisons throughout the tropics were found to be approximately 0.5°C. Confirmed satellite SST data were applied to bleaching events at Bermuda (1988, 1991), Tahiti (1984, 1987, 1991), and Jamaica (1987, 1989, 1990), with a non-bleached site off Belize selected as control. MCSST data showed elevated SSTs coincided with bleaching events both in onset and duration. Bleaching thresholds were developed. An MCSST Degree Heating Weeks (DHW) bleaching index was developed for the Belizean and Jamaican reef sites. A cumulative heating stress of 26 DHW is proposed as the threshold for mass reef bleaching at Belize and Jamaica.

Simulation of remote sensing of sea surface temperature from space: influences of cirrus clouds and stratospheric aerosols on sea surface temperatures derived from the VISSR Atmospheric Sounder

Abstract This simulation study demonstrates that cirrus clouds and volcanic aerosols with atmospheric gases would greatly affect the transmission functions and brightness temperatures of infrared window channels in the VISSR Atmospheric Sounder (VAS), and VAS-derived sea surface temperature (SST) determinations. The ;clear air (CLR) retrieval equations should not be used in the presence of cirrus and high stratospheric aerosol loadings. An alternative five-window channel algorithm could be found that would work in arbitrary clear, cirrus or aerosol conditions, but the retrieval accuracy would decrease in comparison with the multi-channel SST (MCSST) algorithms for simply cirrus clouds, or aerosols only. In MCSST algorithms, channel 12 (3–94μ) is most important for CLR, or tenuous cirrus with any kind of aerosols, or moderate cirrus with weak aerosols, whereas for moderate cirrus combined with the strong aerosol, or dense cirrus with any kind of aerosols, channel 5 (13‐34μ) or channel 8 (11–22μ) becomes the most important. In addition, the effects of variations of water vapour profile, aerosol concentration, and sea surface reflection (SSR) on SST retrievals need to be considered.

The Effects of Shear Flow on Propagation of Rossby Waves in the Equatorial Oceans

Abstract The effects of strong meridional shear of mean flow on propagation of long waves having a wavelength of about 1000 km and period of 25 days observed in the equatorial Pacific and Atlantic Oceans are analyzed in this paper. Information from the weekly multichannel sea surface temperature images derived from the Advanced Very High Resolution Radiometer on board the NOAA series satellites from January 1986 to March 1992 is used for the statistics of the visual parameters of the waves. The characteristic scales of the waves are estimated based on the results by previous investigators and the statistical results of the present study. Solving a potential vorticity equation, the authors obtain a dispersion relation with an additional term depending on the flow shear strength compared with that of the free Rossby wave. The theoretical model provides a good explanation for the variable behavior of long-wave propagation.

Reduction of noise in AVHRR channel 3 data with minimum distortion

The channel 3 data of the Advanced Very High Resolution Radiometer (AVHRR) on the NOAA series of weather satellites (NOAA 6-12) are contaminated by instrumentation noise. The signal to noise ratio (S/N) varies considerably from image to image and the between sensor variation in S/N can be large. The characteristics of the channel noise in the image data are examined using Fourier techniques. A Wiener filtering technique is developed to reduce the noise in the channel 3 image data. The noise and signal power spectra for the Wiener filter are estimated from the channel 3 and channel 4 AVHRR data in a manner which makes the filter adaptive to observed variations in the noise power spectra. Thus, the degree of filtering is dependent upon the level of noise in the original data and the filter is adaptive to variations in noise characteristics. Use of the filtered data to improve image segmentation, labeling in cloud screening algorithms for AVHRR data, and multichannel sea surface temperature (MCSST) estimates is demonstrated. Examples also show that the method can be used with success in land applications. The Wiener filtering model is compared with alternate filtering methods and is shown to be superior in all applications tested. >

Correction to “Sensitivity of satellite multichannel sea surface temperature retrievals to the air‐sea temperature difference” by Douglas A. May and Ronald J. Holyer

Journal of Geophysical Research: OceansVolume 98, Issue C11 p. 20337-20337 CorrectionsFree Access Correction to “Sensitivity of satellite multichannel sea surface temperature retrievals to the air-sea temperature difference” by Douglas A. May and Ronald J. Holyer This article corrects the following: Sensitivity of satellite multichannel sea surface temperature retrievals to the air-sea temperature difference Douglas A. May, Ronald J. Holyer, Volume 98Issue C7Journal of Geophysical Research: Oceans pages: 12567-12577 First Published online: September 20, 2012 Douglas A. May, Douglas A. MaySearch for more papers by this authorRonald J. Holyer, Ronald J. HolyerSearch for more papers by this author Douglas A. May, Douglas A. MaySearch for more papers by this authorRonald J. Holyer, Ronald J. HolyerSearch for more papers by this author First published: 15 November 1993 https://doi.org/10.1029/93JC02077AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume98, IssueC1115 November 1993Pages 20337-20337 RelatedInformation

Sensitivity of satellite multichannel sea surface temperature retrievals to the air‐sea temperature difference

The advanced very high resolution radiometer multichannel sea surface temperature (MCSST) retrieval technique provides global algorithm accuracy statistics generally showing a bias of less than 0.1°C and an rms error of less than 0.7°C when compared to colocated drifting buoy in situ data in the absence of aerosols. This remaining error is not always random but is shown to be correlated to the air‐sea temperature difference. The MCSST technique is modeled and then compared to in situ data to show this dependency. Atmospheric radiative transfer calculations are used to provide a simulation of satellite retrieval sensitivity to air‐sea temperature differences. Buoy sea surface temperature (SST) and air temperature observations are then presented as experimental verification of the simulation results. Retrieval errors depend both on the mean air‐sea temperature difference conditions present in the data set used to empirically derive the algorithm and on the changes in air‐sea temperature difference conditions relative to the derivation data set mean conditions. Retrieval error is found to respond linearly with air‐sea temperature difference changes. MCSST retrieval errors of 1.0°C can occur for air‐sea temperature difference changes of 7°–10°C from mean conditions when the dual‐window (channels 3 and 4) or triple‐window (channels 3, 4, and 5) algorithms are used. The split‐window (channels 4 and 5) MCSST algorithm is shown to be less sensitive to air‐sea temperature differences. Cross‐product SST (CPSST) and nonlinear SST (NLSST) algorithms are also examined. These algorithms generate results similar to the MCSST algorithm for the dual‐ and triple‐window equations. However, the CPSST and NLSST split‐window algorithms demonstrate greater sensitivity to air‐sea temperature difference changes than do the MCSST split‐window algorithm. Retrieval errors of 1°C can occur for air‐sea temperature difference changes of 10°–12°C from mean conditions. Users of satellite SST retrievals in regions that experience large fluctuations in air‐sea temperature difference should be aware of this possible error source.

Comparing stratospheric aerosols from El Chichón and Mount Pinatubo using AVHRR data

One of the key factors in assessing the climatic impact of the Mount Pinatubo eruption of June 15, 1991, is the relative size of this eruption as it compares with other eruptions. As a first approximation, the climatic changes observed after those earlier eruptions can be used to predict the changes to be expected from the more recent eruption. Ideally this intercomparison should be done with a common measurement system. Data from the advanced very high resolution radiometer (AVHRR) onboard the NOAA polar orbiting environmental satellite can be used to compare the optical properties of the aerosol layer produced by the two most recent major volcanic eruptions, El Chichón, early‐April 1982, and Mount Pinatubo, mid‐June 1991. In this paper, we use the error introduced into the multi‐channel sea surface temperature (MCSST) fields by the volcanically‐produced stratospheric aerosol layer to make a relative comparison of the size of the two eruptions. We also use aerosol optical thickness (AOT) estimates from the visible reflectance channel of the AVHRR to verify that the MCSST errors are indeed related to aerosol particle concentration in the stratosphere. During the first three months following both eruptions, these comparisons reveal that Mount Pinatubo introduced slightly less than twice (1.6 to 1.9) the amount of aerosol into the stratosphere as El Chichón.

Use of AVHRR data to verify a system for forecasting diurnal sea surface temperature variability

Abstract Forecasts from an operational system for predicting global diurnal sea surface temperature (SST) variability are compared against multichannel sea surface temperatures calculated from advanced very high resolution radiometer data from the NOAA-9 satellite. The forecast system consists of an upper-ocean model driven by heat fluxes and wind stresses from an operational global weather prediction model. Visual pattern correlations between observed and forecast diurnal changes in SST are generally favourable, indicating that the forecast system is useful. Some systematic deficiencies are also noted: the forecasts do not reproduce the surprisingly sharp boundaries of diurnal warming regions and underpredict the amplitude of the extreme warming events

Temperature and Size Variabilities of the Western Pacific Warm Pool

Variabilities in sea-surface temperature and size of the Western Pacific Warm Pool were tracked with 10 years of satellite multichannel sea-surface temperature observations from 1982 to 1991. The results show that both annual mean sea-surface temperature and the size of the warm pool increased from 1983 to 1987 and fluctuated after 1987. Possible causes of these variations include solar irradiance variabilities, EI Niño-Southern Oscillation events, volcanic activities, and global warming.

Aerosol radiative corrections to the retrieval of sea surface temperatures from infrared radiances measured by the Advanced Very High Resolution Radiometer (AVHRR)

Abstract The radiative effects of atmospheric aerosols on the retrieval of sea surface temperature from the infrared radiances measured in Channels 3(∼ 3·55−3·95µm), 4(∼ 10·30−11·30µm), and 5(∼ 11·50−12·50µm) of the Advanced Very High Resolution Radiometer (AVHRR) onboard the NOAA polar-orbiting operational environmental satellites have been simulated in realistic models of a turbid atmosphere above the sea surface at a given temperature. The LOWTRAN-7 radiative transfer code has been used to compute the upwelling radiances at the central wavenumbers of these three channels. Brightness temperatures computed from these radiances were used in the NOAA/ NESDIS Multichannel Sea Surface Temperature (MCSST) retrieval algorithms to calculate sea surface temperatures. It is observed that the calculated (retrieved) sea surface temperatures are always less than the prescribed value in the model atmosphere, with the depressions ranging up to 4°C, depending upon the type and total columnar abundance of aerosols, prescribed sea surface temperature, and the satellite zenith angle of observation. The modelled sea surface temperature depressions show a high degree of correlation with the line-of-sight aerosol optical thickness; linear regression yields values in excess of 0·8 for the coefficient of determination.