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In order for quantitative applications to make full use of the ever-increasing number of Earth observation satellite systems, data from the various imaging sensors involved must be on a consistent radiometric scale. This paper reports on an investigation of radiometric calibration errors due to differences in spectral response functions between satellite sensors when attempting cross-calibration based on near-simultaneous imaging of common ground targets in analogous spectral bands, a commonly used post-launch calibration methodology. Twenty Earth observation imaging sensors (including coarser and higher spatial resolution sensors) were considered, using the Landsat solar reflective spectral domain as a framework. Scene content was simulated using spectra for four ground target types (Railroad Valley Playa, snow, sand and rangeland), together with various combinations of atmospheric states and illumination geometries. Results were obtained as a function of ground target type, satellite sensor comparison, spectral region, and scene content. Overall, if spectral band difference effects (SBDEs) are not taken into account, the Railroad Valley Playa site is a “good” ground target for cross calibration between most but not all satellite sensors in most but not all spectral regions investigated. “Good” is defined as SBDEs within ± 3%. The other three ground target types considered (snow, sand and rangeland) proved to be more sensitive to uncorrected SBDEs than the RVPN site overall. The spectral characteristics of the scene content (solar irradiance, surface reflectance and atmosphere) are examined in detail to clarify why spectral difference effects arise and why they can be significant when comparing different imaging sensor systems. Atmospheric gas absorption features are identified as being the main source of spectral variability in most spectral regions. The paper concludes with recommendations on spectral data and tools that would facilitate cross-calibration between multiple satellite sensors.

The paper presents the results of an extended analysis of image data sets acquired during the tandem-orbit configuration in 1999 for the purposes of radiometric cross-calibration of the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and Landsat-5 Thematic Mapper (TM) sensors. Earlier work focused on the tandem pair for the Railroad Valley Playa, Nevada (RVPN) site to tie down the Landsat-5 TM calibration based on the more accurate Landsat-7 ETM+ calibration. This paper describes new results based on as many as eight tandem image pairs. The additional tandem images are of primarily vegetated areas for which little or no ground reference data were available. Increasing the number of tandem pairs yielded results for the Landsat 5 TM gain coefficients within approximately ± 1% of the RVPN-based results in spectral bands 1, 2, 3 and 7, and within − 2% and − 4% of the RVPN-based results for spectral bands 4 and 5, respectively.

The calibration of airborne and satellite remote sensing sensors is a fundamental step for the rigorous validation of products derived from satellite data. Because of the inaccessibility of Earth Observation Satellites on orbit, the direct calibration method based on a test site with ground reference data is often considered necessary. However, the problem of radiometric spatial uniformity and temporal stability of test sites constitutes an important issue in the accuracy achieved in calibration operations and the long-term characterization of satellite sensor radiometry. Generally, the coefficient of variation and semivariograms are the most widely used tools for evaluating the radiometric uniformity and stability of a calibration site. In this study, we analyze for the first time the potential of Getis statistics compared to the coefficient of variation for the study of the radiometric spatial uniformity and temporal stability of the Lunar Lake Playa, Nevada (LLPN) test site. The results obtained show the potential and the importance of the synergy generated by these two methods for analyzing the radiometric temporal stability of the LLPN site. Getis statistics provide an excellent spatial analysis of the site while the coefficient of variation provides complementary information on the temporal evolution of the site.

A coordinated effort on the part of several agencies has led to the specification of a definitive radiometric calibration record for the Landsat-5 thematic mapper (TM) for its lifetime since launch in 1984. The time-dependent calibration record for Landsat-5 TM has been placed on the same radiometric scale as the Landsat-7 enhanced thematic mapper plus (ETM+). It has been implemented in the National Landsat Archive Production Systems (NLAPS) in use in North America. This paper documents the results of this collaborative effort and the specifications for the related calibration processing algorithms. The specifications include (i) anchoring of the Landsat-5 TM calibration record to the Landsat-7 ETM+ absolute radiometric calibration, (ii) new time-dependent calibration processing equations and procedures applicable to raw Landsat-5 TM data, and (iii) algorithms for recalibration computations applicable to some of the existing processed datasets in the North American context. The cross-calibration between L...

Significant advancements in Earth observation are expected to come about by developing more systematic capabilities for assimilating remote sensing observations and in situ measurements for use in models, at relevant scales, to generate geophysical and biospheric information products. This paper provides an overview of the role of in situ sensing in the context of integrated Earth sensing. It also defines a framework for taking advantage of intelligent sensorwebs based on the converging technologies of microsensors, computers, and wireless telecommunications in support of critical activities such as the monitoring of remote environments, risk assessment and hazard mapping, and renewable resource information management. The knowledge gleaned from integrated Earth sensing has the potential to empower managers and decision makers to act on critical climate, sustainable development, natural resource, and environmental issues.

Early in its mission, the Landsat-7 spacecraft was temporarily placed in a “tandem” orbit very close to that of the Landsat-5 spacecraft in order to facilitate the establishment of sensor calibration continuity between the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and Landsat-5 Thematic Mapper (TM) sensors. The key period for the tandem configuration was June 1–4, 1999, during which hundreds of nearly coincident matching scenes were recorded by both the Landsat-7 ETM+ and, in cooperation with Space Imaging/EOSAT and international ground stations, the Landsat-5 TM as well. The paper presents a methodology for radiometric cross-calibration of the solar reflective spectral bands of the Landsat-7 ETM+ and Landsat-5 TM sensors and results based on analysis of two different tandem image pairs for which ground reference data are available. With the well-calibrated ETM+ as a reference, the tandem-based cross-calibrations for the two image pairs yield TM responsivities that are consistent to each other to within 2% or better depending on the spectral band. Comparisons with independent methods and results obtained by other groups indicate that the tandem-based cross-calibration is within 3% of the independent results on average in spectral bands 1–4 but compares less favorably in bands 5 and 7. The present study indicates that the tandem cross-calibration approach can provide a valuable “contemporary” calibration update for Landsat-5 TM in the visible and near-infrared spectral bands based on the excellent radiometric performance of Landsat-7 ETM+. The methodology also incorporates adjustments for spectral band differences between the two Landsat sensors. Spectral band difference effects are shown to be more dependent on the surface reflectance spectrum than on atmospheric and illumination conditions. A variety of terrestrial surfaces are assessed regarding their suitability for Landsat radiometric cross-calibration in the absence of surface reflectance spectra.

The paper describes a new methodology that uses spatially extensive hyperspectral imagery as reference data to carry out vicarious radiometric calibrations for multiple satellite sensors. The methodology has been validated using data from a campaign at the Railroad Valley playa test site in Nevada in June 1998. The proof of concept has been further tested based on data acquisition campaigns at the Newell County rangeland test site in Alberta in August and October 1998. The rangeland test site in the Newell County region of Alberta is tested for its suitability as a calibration test site for satellite sensor systems. All three campaigns included ground-based measurements, satellite imagery, and airborne hyperspectral data. The airborne hyperspectral sensor data were acquired using the Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) at Railroad Valley and the Compact Airborne Spectrographic Imager (casi) in all three campaigns. This paper describes the formulation and implementation of the new methodology, and radiometric calibration monitoring results obtained for five different sensors: NOAA-14 AVHRR, OrbView-2 SeaWiFS, SPOT-4 VGT, SPOT-1/2 HRV, and Landsat-5 TM. The results indicate that the nominal on-orbit radiometric calibrations of all the satellite sensors fit within their predicted uncertainties. The combination of both lower-reflectance and higher-reflectance test sites is shown to improve the quality of the calibration monitoring results. In particular, the combined QUASAR monitoring results obtained from the three airborne data acquisition days at the two test sites, encompassing five satellite sensors and a total of 40 spectral band cases, yield a correlation between QUASAR-based and nominal TOA radiances characterized by y=1.026x−1.26, and r2=0.990. Temporal extensions of QUASAR data sets to calibrate satellite sensors imaging the test site one or more days away from the airborne data acquisition day yield mixed results.

RESUMELe systeme de geocodage et de composition (GeoComp-n) du Centre canadien de teledetection (CCT) sert a traiter les donnees de ht serie des satellites porteurs de radiometres perfectionnes a tres haut pouvoir de resolution (AVHRR) de la National Oceanic and Atmospheric Administration (NOAA) des Etats-Unis. Le systeme GeoComp-n produit des cartes composees monodates ou multidates de la reflectance de la surface de la masse continentale canadienne dans les bandes spectrales du visible et du proche infrarouge a une resolution spatiale de 1 km. Les donnees doivent d'abord etre traitees en unites geophysiques exactes pour permettre l'utilisation de ces cartes et des produits derives dans te cadre de diverses etudes du changement climatique planetaire et de la couverture terrestre. Dans le cas des donnees de satellites, cela exige non seulement un etalonnage radiometrique exact, mais egalement l'application aux donnees d'images de la correction appropriee des effets atmospheriques. L'epaisseur optique des ...

RESUMEL'utilisation des donnees de teledetection pour des analyses quantitatives, multitemporelles et multicapteurs necessite un etalonnage radiometrique fiable. Un mauvais etalonnage peut introduire jusqu'a 50 % d'erreur dans l'evaluation des elements biophysiques au sal. Malgre les efforts considerables deployes durant les deux dernieres decennies dans ce domaine, il arrive encore que certains utilisateurs ne s'occupent guere de l'etalonnage radiometrique et de la standardisation des donnees dans diverses applications de la teledetection. Pour l'obtention de donnees radiometriques de qualite, avec assurance et comparable dans le temps, et pour l'optimisation des performances de la teledetection des ressources terrestres, un etalonnage radiometrique adequat est indispensable. Cette etude discute de l'etalonnage relatif et absolu des capteurs optiques, de la degradation temporelle de leur qualite radiometrique en orbite et des facteurs qui controlent la precision de l'etalonnage. Ainsi, des exemples sont ...

RESUMEL'etape d'etalonnage et de validation des donnees de teledetection (cal/val) est essentielle pour la production de donnees fiables en teledetection. La correction atmospherique permet d'obtenir les proprietes intrinseques de la surface (en particulier le facteur de reflectance bidirectionnelle (FRB) a la surface) a partir des images acquises a altitude (FRB apparent au capteur) et constitue de ce fait un element primordial de cette procedure d'etalonnage et de validation (cal/val). Il est donc necessaire de disposer d'un moyen standard d'estimation de l'erreur sur la procedure d'obtention du FRB a la surface. Nous presentons ici les concepts fondamentaux necessaires au developpement d'un tel modele d'erreur spectrale qui, nous l'esperons, permettra d'estimer l'erreur pour une procedure de correction atmospherique quelconque.

RESUMELa synthese de certains des principaux sujets d'interet dans le domaine de l'etalonnage/validation (etal/val) permet d'identifier des secteurs ou des ameliorations devront etre apportees a la procedure cal/val pour atteindre un niveau operationnel du point de vue de l'utilisateur. Des axes specifiques de recherche et de developpement sont discutes dans le domaine optique notamment en ce qui concerne l'etalonnage radiometrique des capteurs, la correction atmospherique, la caracterisation spectrale et l'influence des effets geometriques sur la radiometrie de l'image.

Vegetation indices derived from satellite image data have become one o f the primary information sources for monitoring vegetation conditions and mapping land cover change. The most widely used vegetation index in this context is NDVI, the normalized difference vegetation index, which is a function of red and near-infrared spectral bands. Given that the spectral and spatial of imagery in the red and near-infrared vary from sensor to sensor, NDVI values based on data from different instruments will not be directly comparable. The present study demonstrates the impact of changes in spectral bandwidth and spatial scale on NDVI derived from Airborne VisiblelInfrared Imaging Spectrometer (AVIRIS) data acquired at 20-m resolution over a forested region in southeastern British Columbia. For this purpose, the 10-nm AVIRIS data were spectrally and spatially aggregated in the red and near-infrared to simulate bandwidths from 10 nm to 150 nm for ground resolutions varying from 20 m to 1100 m. Sensor-specific spectral bands and spatial resolutions such as those for SPOT HRV, Landsat TM, NOAA AVHRR, EOS MODIS, and Envisat MERIS were also generated. NDVI values were then calculated using atmospherically corrected surface reflectances for forestry-related targets for the entire simulated band set at the various scales. The results indicate that the NDVI is significantly affected by differences in spectral bandwidth, especially for the red band, and that changes in spatial resolution lead to less peruasive but more land cover specific effects on NDVI. Results for the forested regions also indicate that NDVI is not very sensitive to the location of the near-infrared spectral band, provided that the bandwidth is no wider than 50 nm and the atmospheric correction for water vapor absorption is adequate. If either proviso is relaxed, the wavelength placement of the near-infrared spectral band is more critical, the optimum location being in the 850–880 nm range. Finally, for the same forest targets, some results were also generated for several other vegetation indices that make straightforward use of atmospherically corrected red and near-infrared spectral bands.

RESUMELe present article donne un apercu de la methode de correction atmospherique fondee sur des cibles sombres pour l'estimation de l'epaisseur optique des aerosols. Cette methode fait intervenir des calculs relativement nombreux sur les parametres atmospheriques, contrairement a la methode plus repandue de correction atmospherique qui procede par soustraction des cibles sombres et qui par nature est plus approximative et ne requiert pas de renseignements supplementaires sur les conditions atmospheriques. Les elements descriptifs d'un algorithme utilisant des cibles sombres applicable aux donnees obtenues a partir du capteur thematique de Landsat sont presentes en fonction de trois operations principales liees au flux de donnees: extraction de la valeur numerique des cibles sombres, conversion en valeurs de reflectance et determination de l'epaisseur optique des aerosols. Les incertitudes cles entourant cette methode resident dans les valeurs de reflectance supposees de la surface des cibles sombres dan...

RESUMELe Centre canadien de teledetection a mis sur pied un programme de recherche qui permettra de mieux comprendre les effets radiometriques sur une scene obtenue par teledetection, dus a des elements tels que l'atmosphere et la dependance entre la geometrie et la reflectance de surface (effets georadiometriques). Cet article presente un projet de recherche sur les effets georadiometriques (GEORAD) et decrit, notamment, les travaux de terrain effectues dans le but de recueillir les donnees necessaires a l'elaboration et a la validation d'un modele de reflectance du couvert forestier qui permette de deduire la fonction de distribution de reflectance bidirectionnelle du couvert forestier et des elements de ce dernier, pour utilisation dans l'interpretation des images de moyenne a haute resolution, obtenues par teledetection.

RESUMEUne simulation de donnees du spectroradiometre MODIS-EOS a ete effectuee spectralement et spatialement a l'aide d'une serie de donnees AVIRIS d'un terrain montagneux situe en Colombie-Britannique. L'influence des variations atmospheriques dues a l'elevation du terrain sur les indices de vegetation calcules a partir des donnees AVHRR et des donnees simulees MODIS a ete etudiee. Les resultats montrent qu'il existe une dependance importante entre l'elevation du terrain et l'indice de vegetation par difference normalisee (IVDN) et que celle-ci augmente proportionnellement a la diminution de la densite de la vegetation.

Radiometric and atmospheric corrections are formulated with a view to computing vegetation indices such as the Normalized Difference Vegetation Index (NDVI) from surface reflectances rather than the digital signal levels recorded at the sensor. In particular, look-up table (LUT) results from an atmospheric radiative transfer code are used to save time and avoid the complexities of running and maintaining such a code in a production environment. The data flow for radiometric image correction is very similar to commonly used geometric correction data flows. The role of terrain elevation in the atmospheric correction process is discussed and the effect of topography on NDVI is highlighted.

Integration of meteorological and remote sensing data in crop growth models offers a potentially powerful tool for yield monitoring. Leaf area index (LAI) is a key variable in crop growth models. The derivation of reliable LAI maps from satellite imagery would provide a means of spatially extrapolating these models. As part of a two-year project to develop an intelligent sensorweb system for yield prediction in agricultural crops and rangeland, the ability to obtain reliable LAI estimates from Compact High Resolution Imaging Spectrometer (CHRIS) data was investigated. Throughout the 2004 and 2005 growing season, data from the CHRIS sensor were acquired over two contrasting sites in Alberta, a wheat crop and rangeland. The modified triangular vegetation index (MTVI2) was used to derive LAI values which were compared to ground- based LAI data collected weekly or tri-weekly in wheat and monthly on the rangeland. A strong relationship was observed between ground-based and remote sensing derived LAI in the case of wheat (r=0.91-0.93). In, the rangeland, where senescent vegetation is a confounding factor, LAI was consistently overestimated using the CHRIS imagery.

Differences between the analogous spectral bands on Landsat-class sensors can have significant impacts on vegetation index comparisons. Vegetation indices based on satellite image data are widely used for change monitoring but, when derived from different satellite sensors, they will differ as a function of the uncorrectable differences between the analogous spectral bands used to generate the vegetation indices. This issue becomes important as available satellite sensors in the Landsat class are being considered in order to fill the anticipated gap in continuity of the Landsat TM and ETM+ data record. A follow-on mission is not expected any earlier than 2011. Among the current imagers examined in this study, which encompassed four vegetation targets and eight vegetation indices, either one of the IRS-P6 sensors or the SPOT-5 HRG is preferable to the CBERS- 2 HRCC as a replacement sensor from the standpoint of agreement with Landsat-based vegetation indices. Among the vegetation indices considered, the Global Environmental Monitoring Index (GEMI) proved to be the least sensitive to spectral dissimilarities between sensors and hence GEMI is worth considering for quantitative monitoring of environmental change using images from multiple sensors to fill the Landsat data archive.

The paper presents the results of an extended analysis of image data sets acquired during the tandem-orbit configuration in 1999 for the purposes of radiometric cross-calibration of the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and Landsat-5 Thematic Mapper (TM) sensors. Earlier work focused on the tandem pair for the Railroad Valley Playa, Nevada (RVPN) site to tie down the Landsat-5 TM calibration based on the more accurate Landsat-7 ETM+ calibration. This paper describes new results based on as many as eight tandem image pairs. The additional tandem images are of vegetated areas for which little or no ground reference data were available. Increasing the number of tandem pairs yielded results for the Landsat 5 TM gain coefficients within approximately ± 1 % of the RVPN-based results in spectral bands 1, 2, 3 and 7, and within -2 % and -4 % of the RVPN-based results for spectral bands 4 and 5, respectively.

In this study, we present a new vegetation index, the TDVI: transformed difference vegetation index. This index shows the same sensitivity as the soil adjusted vegetation index (SAVI) to the optical proprieties of bare soil subjacent to the cover. It does not saturate like NDVI and SAVI and it shows an excellent linearity as a function of the rate of vegetation cover.

The Flood Information Management System (FIMS) represents the confluence of several cutting edge technologies and methodologies. The FIMS website combines real-time in situ data, internationally recognized hydraulic and hydrologic models, multiresolution remotely sensed images and a customized Web interface all within one coherent and easily accessible Internet location. The FIMS prototype development focused on two river basins with active river monitoring programs, the Fraser River in British Columbia and the St. John River in New Brunswick. Near-real-time sensors in both these river basins provide FIMS with its water quantity baseline data. Web-based software engineering provides the bridge between hydraulic/hydrologic models and the graphical user interfaces used to display the near-real-time geospatial results on the Internet. Users are able to interactively visualise Ikonos, Radarsat, and Landsat image maps of their areas, visualize hydrometric station locations and actual flow data, then run models that show flood hazard, risk and extents based on current and predicted flows.

We present the technical implementation details for a prototype central atmospheric correction parameter server called NOMAD (Networked On-line Mapping of Atmospheric Data). Using a Web service, aerosol optical depth (AOD) values are transmitted via the network to a Web service aware atmospheric correction application. Information about the date and location of the image are extracted automatically from the image, allowing a best estimate of AOD at 500 nm to be retrieved from the central server database. A Web service approach was adopted to allow easy cross platform development in multiple software languages. Using the Web Services Definition Language (WSDL) description of the atmospheric correction parameter server Web service, application developers can easily make their atmospheric correction applications "Web aware". On the server side, researchers maintaining the central database are free to concentrate on providing the best quality data available.

Reports on research to adapt the 2/sup nd/ Generation Prairie Agrometeorological Model for wheat developed by Raddatz (1993) at Environment Canada to use both in situ data from a distributed network of meteorological stations (original mode) and NOAA AVHRR information output from the GeoComp-N processor at the Manitoba Remote Sensing Centre. Two parameters previously approximated by the model have been substituted with AVHRR derived information: fractional leaf area, and skin temperature. These parameters are critical for obtaining accurate outputs. Model outputs were ingested into a GIS to generate maps of crop growth stage expressed as biometeorological time, actual evapotranspiration or crop water-use, and top zone and root zone soil moisture for a test area in southern Manitoba for the year 2000 growing season.

[1] Atmospheric water vapor is a key parameter for the analysis of climatic systems (greenhouse gas effect), in particular over high latitudes where water vapor displays an important seasonal variability. The sparse spatial and temporal sampling of atmospheric water vapor observations across Canada needs to be improved. A series of instruments and methods including a 940-nm solar absorption band radiometer (R) and radiosonde (S) analysis from a numerical weather prediction model and a ground-based bi-frequency Global Positioning System (GPS) were used to evaluate the integrated atmospheric water vapor (IWV) at various sites in Canada and Alaska from a multiyear database. The IWV-R measurements were collected within the framework of the North American Sun Radiometry network (AERONET/AEROCAN). Intercomparisons between [IWV-GPS and IWV-S], [IWV-R and IWV-GPS], and [IWV-R and IWV-S] show root mean square (RMS) differences of 1.8, 1.9, and 2.2 kg m � 2 , respectively. GPS meteorology appears to be the easiest approach to calibrate the solar radiometer water vapor band owing to its flexibility, and it allows us to overcome the Sun radiometry limitation in high-latitude areas like the Arctic. The sensitivity of the GPS retrieval to various parameters like GPS satellite constellation and meteorological data are discussed. The classical linear relationship between the surface temperature and the integrated weighted mean temperature profile needed for IWV-GPS retrieval may be significantly different for Arctic air masses compared with midlatitude air masses in the case of tropospheric temperature profile inversion. An ever-expanding multiyear (1994–2001) North American summer water vapor climatology, derived from AERONET/Canadian Sun Radiometer Network, is presented and analyzed, showing a mean value of 19.8 ± 6.1 kg m � 2 and variations from 17 kg m � 2 in Alaska to 23 kg m � 2 in southeastern Canada. The results in Bonanza Creek, Alaska, show significant interannual variations with a peak in 1997, which may

Surface reflectance retrieval from imaging spectrometer data has become important for quantitative information extraction in many application areas. In order to calculate surface reflectance from remotely measured radiance, radiative transfer codes play an important role for removal of the scattering and gaseous absorption effects of the atmosphere. The present study evaluates surface reflectances retrieved from airborne visible/infrared imaging spectrometer (AVIRIS) data using three radiative transfer codes: modified 5S (M5S), 6S, and MODTRAN2. Comparisons of the retrieved surface reflectance with ground-based reflectance were made for different target types such as asphalt, gravel, grass/soil mixture (soccer field), and water (Sooke Lake). The results indicate that the estimation of the atmospheric water vapor content is important for an accurate surface reflectance retrieval regardless of the radiative transfer code used. For the present atmospheric conditions, a difference of 0.1 in aerosol optical depth had little impact on the retrieved surface reflectance. The performance of MODTRAN2 is superior in the gas absorption regions compared to M5S and 6S.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Bidirectional reflectance factors (BRF) for a pecan orchard have been studied using Advanced Solid-State Array Spectrometer (ASAS) data acquired in the solar principal plane at altitudes of 2300 m and 5300 m above ground. In particular, the angular dependency of the BRF of different targets such as sunlit and shaded portions of the pecan tree, orchard floor, and soil (road) have been studied for viewing directions between -45 degrees and +45 degrees. The results indicate in general an increasing reflectance from the forward scattering direction to the backscattering direction. In addition, an increase in pixel size has significant effects on the surface BRFs.

A procedure is formulated to investigate the sensitivity of surface reflectances retrieved from satellite sensor data to uncertainties in aerosol optical properties. Aerosol optical characteristics encompassed in the study include the Junge parameter (i.e., spectral dependence), the imaginary part of the refractive index (i.e., aerosol absorption), and the aerosol optical depth. Key results for a wavelength of 0.550 micrometers are presented graphically in terms of accuracy requirements on the aerosol property under consideration for a 5 uncertainty in predicted surface reflectance.

We formulate a procedure to investigate the sensitivity of surface reflectances retrieved from satellite sensor data to uncertainties in aerosol optical properties. Aerosol optical characteristics encompassed in the study include the aerosol optical depth, the Junge parameter (i.e., spectral dependence), and the imaginary part of the refractive index (i.e., aerosol absorption). The study includes both clear and hazy atmospheric conditions, wavelengths of 0.550 and 0.870 µm, three solar zenith angles, and five viewing geometries. Key results are presented graphically in terms of accuracy requirements on the aerosol property under consideration for a 5% uncertainty in predicted surface reflectance.

This article reviews experience in radiometric corrections of satellite and airborne remote sensing data at the Canada Centre for Remote Sensing (CCRS) during the period 1972 to 1986. It also describes current research areas and recommends areas of future research where high priority is important for global change monitoring and for the derivation of quantitative information from remotely-sensed data in the solar reflective spectral regions. Throughout its history, CCRS has directed its efforts towards meeting specific needs. For satellite data (Landsat MSS, Thematic Mapper, AVHRR, and now SPOT HRV), the progression has been from relative calibration of detector elements (destriping) to absolute radiometric calibration of digital data. The routine use of atmospheric corrections and a priori knowledge of terrain reflectance properties have been introduced into the generation of specialized digital enhancements for photographic products. This has required the investigation of a wide range of radiom...