Spatio-temporal constraints for emissivity and surface temperature retrieval: Preliminary results and comparisons for SEVIRI and IASI observation

Infrared instrumentation on geostationary satellites is now rapidly approaching the spectral quality and accuracy of modern sensors flying on polar platforms. Currently, the core of EUMETSAT geostationary meteorological programme is the Meteosat Second Generation (MSG). However, EUMETSAT is preparing for the Meteosat Third Generation (MTG). The capability of geostationary satellites to resolve the diurnal cycle and hence to provide time-resolved sequences or times series of observations is a source of information which could suitably constrain the derivation of geophysical parameters. Nowadays, also because of lack of time continuity, when dealing with observations from polar platforms, the problem of deriving geophysical parameters is normally solved by considering each single observation as independent of past and future events. For historical reason, the same approach is currently pursued with geostationary observations, which are still being dealt with as they were with polar observations. In this study we show some preliminary results on emissivity and surface temperature retrieval for SEVIRI observations, using the Kalman filter methodology (KF) and compare the retrievals with those obtained using IASI observations co-localized with SEVIRI ones using the times accumulation approach (Optimal Estimation OE). The Sahara desert was chosen as target area, and both SEVIRI and IASI data (infrared radiances and cloud mask) were acquired. The time period considered is that of July 2010 (the whole month). ECMWF analyses for the same date and target area have also been acquired, which comprise Ts, T(p), O(p), Q(p) for the canonical hours 0:00, 6:00, 12:00 and 18:00. Moreover, for the purpose of developing a suitable background for emissivity, the Global Infrared Land Surface Emissivity database developed at CIMSS, University of Wisconsin, derived by MODIS observations was used and was available from the year 2003 till 2011. Concerning the performance of the two methodologies, the retrieval of skin temperature is almost equivalent. The agreement between OE and KF is fairly good if compared with ECMWF analysis for sea surface, while for land surface, OE and KF agree fairly well with ECMWF during the night, but at midday ECMWF shows a cold bias of 10 K and more. For emissivity the comparison with the UW/BFEMIS database for the same date and location is fairly good for both methods

ASSESSING THE IMPACT OF INCORRECT OBSERVATIONAL COVARIANCE MATRIX OVER RETRIEVAL: METHODS AND APPLICATION TO IASI DATA

The paper addresses the effect of an incorrect specified observational covariance matrix on the retrieval of atmospheric parameters from high spectral resolution infrared radiances. The case of a non-diagonal covariance matrix approximated with its diagonal is dealt with. The problem is of interest to IASI (Infrared Atmospheric Sounding Interferometer) which, because of apodization, is characterized by a non-diagonal covariance matrix. However, the diagonal alone rather than the full matrix is normally used in data assimilation and retrieval schemes because of numerical and computational efficiency. The problem will be analysed in its formal, mathematical aspects through the help of the linear approximation. In addition, a series of retrieval exercises will help to draw more general conclusions. We have found that the incorrect use of the diagonal instead of the full covariance matrix can affect the spatial vertical resolution of the retrieval and can lead to instability in the final solution, especially in the lower troposphere

Estimation of soil and vegetation temperatures with multiangular thermal infrared observations: IMGRASS, HEIFE, and SGP 1997 experiments

The potential of directional observations in the thermal infrared region for land surface studies is a largely uncharted area of research. The availability of the dual-view Along Track Scanning Radiometer (ATSR) observations led to explore new opportunities in this direction. In the context of studies on heat transfer at heterogeneous land surfaces, multiangular thermal infrared (TIR) observations offer the opportunity of overcoming fundamental difficulties in modeling sparse canopies. Three case studies were performed on the estimation of the component temperatures of foliage and soil. The first one included the use of multi-temporal field measurements at view angles of 0°, 23° and 52°. The second and third one were done with directional ATSR observations at view angles of 0° and 53° only. The first one was a contribution to the Inner-Mongolia Grassland Atmosphere Surface Study (IMGRASS) experiment in China, the second to the Hei He International Field Experiment (HEIFE) in China and the third one to the Southern Great Plains 1997 (SGP 1997) experiment in Oklahoma, United States. The IMGRASS experiment provided useful insights on the applicability of a simple linear mixture model to the analysis of observed radiance. The HEIFE case study was focused on the large oasis of Zhang-Ye and led to useful estimates of soil and vegetation temperatures. The SGP 1997 contributed a better understanding of the impact of spatial heterogeneity on the accuracy of retrieved foliage and soil temperatures. Limitations in the approach due to varying radiative and boundary layer forcing and to the difference in spatial resolution between the forward and the nadir view are evaluated through a combination of modeling studies and analysis of field data

SEAPAK user's guide, version 2.0. Volume 2: Descriptions of programs

The SEAPAK is a user-interactive satellite data analysis package that was developed for the processing and interpretation of Nimbus-7/Coastal Zone Color Scanner (CZCS) and the NOAA Advanced Very High Resolution Radiometer (AVHRR) data. Significant revisions were made since version 1.0, and the ancillary environmental data analysis module was greatly expanded. The package continues to be user friendly and user interactive. Also, because the scientific goals of the ocean color research being conducted have shifted to large space and time scales, batch processing capabilities for both satellite and ancillary environmental data analyses were enhanced, thus allowing for large quantities of data to be ingested and analyzed

An Instrument Anomaly in the Mars Exploration Rover Panoramic Camera (Pancam) 1009 nm Filter (R7): Characterisation, Simulation, Correction and Preliminary Verification

During pre‐flight calibration of the panoramic camera (Pancam) instrument on board the Mars Exploration Rovers MER A (Spirit) and MER B (Opportunity), a discrepancy was noted between 11‐band spectra extracted from Pancam images of the camera's radiometric calibration target and reflectance spectra obtained with a spectrometer. This discrepancy was observed in the longest‐wavelength filter of the camera (the longpass R7 filter with system λ_(eff) = 1,009 nm) and consisted of a reduction in contrast between bright and dark regions. Here we describe and characterize this effect. We propose that the effect arises because long‐wavelength photons close to the silicon band‐gap at 1,100 nm are allowed through the R7 filter, pass through the bulk charge‐coupled device, scatter from the backside, pass through the charge‐coupled device again, and are registered in a pixel other than the pixel through which they originally entered. Based on this hypothesis we develop a model capable of accurately simulating the effect, and correct for it. We present preliminary results from testing this correction on preflight, as well as in‐flight, images. The effect is small, but in some specific cases in small regions of high contrast, the effect is significant. In in‐flight images of Martian terrain we observed the signal in dark shadows to be artificially inflated by up to ∼ 33% and analysis of early‐mission calibration target images indicated that the reduced contrast due to the artifact is equivalent to >100 DN (full well = 4095 DN) for a hypothetical perfectly dark pixel