Analysis of Long-Term Cloud Cover, Radiative Fluxes, and Sea Surface Temperature in the Eastern Tropical Pacific

Grant activities accomplished during this reporting period are summarized. The contributions of the principle investigator are reported under four categories: (1) AHVRR (Advanced Very High Resolution Radiometer) data; (2) GOES (Geostationary Operational Environ Satellite) data; (3) system software design; and (4) ATSR (Along Track Scanning Radiometer) data. The contributions of the associate investigator are reported for:(1) longwave irradiance at the surface; (2) methods to derive surface short-wave irradiance; and (3) estimating PAR (photo-synthetically active radiation) surface. Several papers have resulted. Abstracts for each paper are provided

Impact of AVHRR channel 3b noise on climate data records: filtering method applied to the CM SAF CLARA-A2 data record

A method for reducing the impact of noise in the 3.7 micron spectral channel in climate data records derived from coarse resolution (4 km) global measurements from the Advanced Very High Resolution Radiometer (AVHRR) data is presented. A dynamic size-varying median filter is applied to measurements guided by measured noise levels and scene temperatures for individual AVHRR sensors on historic National Oceanic and Atmospheric Administration (NOAA) polar orbiting satellites in the period 1982–2001. The method was used in the preparation of the CM SAF cLoud, Albedo and surface RAdiation dataset from AVHRR data—Second Edition (CLARA-A2), a cloud climate data record produced by the EUMETSAT Satellite Application Facility for Climate Monitoring (CM SAF), as well as in the preparation of the corresponding AVHRR-based datasets produced by the European Space Agency (ESA) Climate Change Initiative (CCI) project ESA-CLOUD-CCI. The impact of the noise filter was equivalent to removing an artificial decreasing trend in global cloud cover of 1–2% per decade in the studied period, mainly explained by the very high noise levels experienced in data from the first satellites in the series (NOAA-7 and NOAA-9). View Full-Tex

A procedure for the detection and removal of cloud shadow from AVHRR data over land.

Abstract-Although the accurate detection of cloud shadow in AVHRR scenes is important for many atmospheric and terrestrial applications, relatively little work in this area has appeared in the literature. This paper presents a new multispectral algorithm for cloud shadow detection and removal in daytime AVHRR scenes over land. It uses a combination of geometric and optical constraints, derived from the pixel-by-pixel cross-track geometry of the scene and image analysis methods to detect cloud shadow. The procedure works well in tropical and midlatitude regions under varying atmospheric conditions (wet-dry) and with different types of terrain. Results also show that underdetected cloud shadow can produce errors of 30-40% in observed reflectances for affected pixels. Moreover, radiative transfer calculations show that the effects of cloud shadow are comparable to or exceed those of aerosol contamination for affected pixels. The procedure is computationally efficient and hence could be used to produce improved weather forecast, land cover, and land analysis products. The method is not intended for use under conditions of poor solar illumination and/or poor viewing geometry

Application of multi-window maximum cross-correlation to the mediterranean sea circulation by using MODIS data

In a previous study an improved Maximum Cross-Correlation technique, called Multi-Window Maximum Cross-Correlation (MW-MCC), was proposed, and applied to noise-free synthetic images in order to show its potential and limits in oceanographic applications. In this work, instead, the application of MW-MCC to high resolution MODIS images, and its capability to provide useful and realistic results for ocean currents, is studied. When applied to real satellite images, the MW-MCC is subject to cloud cover and image quality problems. As a consequence the number of useful MODIS images is greatly reduced. However, for every MODIS image, multiple spec-tral bands are available, and it is possible to apply the MW-MCC algorithm to the same scene as many times as the number of these bands, increasing the possibility of finding valid current vectors. Moreover, the comparison among the results from different spectral bands allows to verify both the consistency of the computed current vectors and the validity of using a spectral band as a good tracer for the ocean circulation. Due to the lack of systematic current measurements in the area considered, it has been not possible to perform an ex-tensive error analysis of the MW-MCC results, although a case study of a comparison between HF radar measurements and MW-MCC data is shown. Moreover, some comparison between numerical ocean model simulations and MW-MCC results are also shown. The coherence of the resulting circulation flow, the high number of current vectors found, the agreement among different spectral bands, and conformity with the currents measured by the HF radars or simulated by hydrodynamic models show the validity of the technique

The Evaluation of Multichannel Shortwave Infrared (SWIR) Optical Data from the Japanese Earth Resources Satellite (JERS-1), for Geological Applications

The primary objective of this thesis is to evaluate data from the Japanese Earth Resources Satellite (JERS-1), particularly multi-channel shortwave infrared (SWIR) data. These data are to be evaluated in comparison with Landsat Thematic Mapper (TM) data for geological applications, in particular lithological discrimination in an arid environment (Oman) and volcano monitoring (Lascar, Chile). JERS-1 is the first satellite purposely designed for geological remote sensing. Optical data (OPS) acquired by JERS-1 is of a higher spatial and spectral resolution than that from-Landsat TM. Unfortunately the immediate benefits of this higher resolution are lost due to the low quality of all OPS data. All seven OPS channels are affected by along- and across-track striping, image blur at spectral boundaries, poor dynamic ranges, random speckle and inter-channel misregistration. Poor data quality greatly reduces the geological potential of these data, especially as the most severely corrupted channels are OPS 6 and OPS 7, two of the new narrow SWIR channels. However, despite poor data quality the majority of the noise artefacts associated with these data can be either removed or significantly reduced by processing in the frequency domain. A number of frequency domain techmques have been developed which separate noise features from real image data. These techniques greatly improve the quality of most OPS channels, although OPS 6 and OPS 7 are sometimes beyond recovery. The spectral characteristics of the lithologies comprising the Oman ophiolite complex are used to demonstrate the increased discrimination potential of ‘cleaned’ multichannel OPS data. High resolution lab spectra of the ophiolite lithologies were degraded to TM and OPS spectral resolutions in order to determine the influence of spectral resolution on lithologie discrimination. The results of this comparison indicated that a lot of discrimination information seen at lab resolution is lost at OPS and TM resolution. This results in the reflectance spectra of some ophiolite lithologies appearing very similar, especially at TM resolution. More discrimination information is preserved at OPS resolution due to the sub-division of the wavelength range equivalent to TM 7 into three narrow discrete channels. Analysis of resampled spectra at OPS resolution shows that OPS 8 conrtbutes new spectral information not discernible at TM resolution. Resampled lab spectra at OPS resolution were used to try to develop effective band combinations and image processing techniques capable of discriminating ophiolite lithologies. Tests of OPS band composites indicated that the best composite was one which combined three bands from spectrally distinct parts of the spectrum. OPS 852 proved to be the most effective OPS composite, discriminating the majority of ophilite lithologies. Analysis of both spectral and image data showed that OPS 6 and OPS 7 are highly correlated for ophiolite lithologies. Composites combining both of these channels were very poor, however combining one channel (usually OPS 6 due to quality) with OPS 8 and OPS 2 produced a reasonable composite (OPS 862). OPS 852 is the most informative composite, and would remain so even if OPS 6 and OPS 7 were of a higher quality. Comparisons with the best TM composite (TM 754 decorrelation stretched) showed that the OPS data discriminated more lithologies and often allowed previously mapped units to be sub-divided. To test the potential of OPS data for volcano monitoring a time series of four OPS scenes, straddling the April 1993 eruption of Lascar (Chile), were analysed. This study showed that the higher spatial resolution of the OPS sensor was capable of detecting smaller thermal features than possible with TM. This resulted in four intra-crater maps of thermal anomolies being produced, showing thermal variations associated with periods of dome growth and collapse. These data also demonstrated their usefulness for mapping the extent of pyroclastic deposits emplaced during this eruption, and also their subsequent rapid erosion. Overall OPS data are shown to offer significant improvements with respect to lithological mapping and volcano monitoring despite their greatly reduced quality compared with Landsat TM. Extensive tests of various band combinations and processing techniques show that some of the most informative images derived of the ophiolite lithologies consist simply of cleaned channels of data combined as false colour composites. The effectiveness and possible advantages of advanced image processing techniques are often negligible due to the rapid degradation of the data when subjected to intensive processing. OPS 8 is the channel mainly responsible for contributing additional new valuable spectral information, that is not available from Landsat TM. The slight increases in spatial and spectral resolution offered by OPS data result in significantly more geological information being discernible from an OPS composite than on the equivalent TM composite

Half a century of satellite remote sensing of sea-surface temperature

Sea-surface temperature (SST) was one of the first ocean variables to be studied from earth observation satellites. Pioneering images from infrared scanning radiometers revealed the complexity of the surface temperature fields, but these were derived from radiance measurements at orbital heights and included the effects of the intervening atmosphere. Corrections for the effects of the atmosphere to make quantitative estimates of the SST became possible when radiometers with multiple infrared channels were deployed in 1979. At the same time, imaging microwave radiometers with SST capabilities were also flown. Since then, SST has been derived from infrared and microwave radiometers on polar orbiting satellites and from infrared radiometers on geostationary spacecraft. As the performances of satellite radiometers and SST retrieval algorithms improved, accurate, global, high resolution, frequently sampled SST fields became fundamental to many research and operational activities. Here we provide an overview of the physics of the derivation of SST and the history of the development of satellite instruments over half a century. As demonstrated accuracies increased, they stimulated scientific research into the oceans, the coupled ocean-atmosphere system and the climate. We provide brief overviews of the development of some applications, including the feasibility of generating Climate Data Records. We summarize the important role of the Group for High Resolution SST (GHRSST) in providing a forum for scientists and operational practitioners to discuss problems and results, and to help coordinate activities world-wide, including alignment of data formatting and protocols and research. The challenges of burgeoning data volumes, data distribution and analysis have benefited from simultaneous progress in computing power, high capacity storage, and communications over the Internet, so we summarize the development and current capabilities of data archives. We conclude with an outlook of developments anticipated in the next decade or so