Radiance Coefficient Research Articles

Marine coastal zones monitoring by shipborne semiautomatic passive optical complex

ABSTRACTFor studying of the environmental status of marine coastal areas, it is often necessary to obtain operatively detailed data about water constituents and their distribution over the area. The three-channel passive optical complex for Ecological Monitoring of Marine Areas (EMMA), developed by us, was applied in the Feodosia Bay, the Black Sea, to obtain remotely the absorption indices for the suspended matter, coloured dissolved organic matter, and phytoplankton pigments. It operated from board a vessel for more than 4 h and gave data for approximately 15,000 sea radiance coefficient spectra. The obtained spectra were processed by the original method giving possibility to suppress negative influence of the weather and experiment conditions and to get the absorption index spectra of the water constituents. The data of shipborne remote sensing using EMMA were compared to the estimates retrieved from the measurements on water samples taken at special stations on the route; their correlation turned out to be quite reasonable. The distributions of the suspended matter and coloured organic matter, obtained remotely over the studied area, were discussed. This research showed the possibility of EMMA application for ground truth measurements and for exploring the sea areas close to the coastal line, which cannot be seen from satellites because of cloudiness.

Updating Absolute Radiometric Characteristics for KOMPSAT-3 and KOMPSAT-3A Multispectral Imaging Sensors Using Well-Characterized Pseudo-Invariant Tarps and Microtops II

Radiometric calibration of satellite imaging sensors should be performed periodically to account for the effect of sensor degradation in the space environment on image accuracy. In this study, we performed vicarious radiometric calibrations (relying on in situ data) of multispectral imaging sensors on the Korea multi-purpose satellite-3 and -3A (KOMPSAT-3 and -3A) to adjust the existing radiometric conversion coefficients according to time delay integration (TDI) adjustments and sensor degradation over time. The Second Simulation of a Satellite Signal in the Solar Spectrum (6S) radiative transfer model was used to obtain theoretical top of atmosphere radiances for both satellites. As input parameters for the 6S model, surface reflectance values of well-characterized pseudo-invariant tarps were measured using dual ASD FieldSpec® 3 hyperspectral radiometers, and atmospheric conditions were measured using Microtops II® Sunphotometer and Ozonometer. We updated the digital number (DN) of the radiance coefficients of the satellites; these had been used to calibrate the sensors during in-orbit test periods in 2013 and 2015. The coefficients of determination, R2, values between observed DNs of the sensors, and simulated radiances for the tarps were more than 0.999. The calibration errors were approximately 5.7% based on manifested error sources. We expect that the updated coefficients will be an important reference for KOMPSAT-3 and -3A users.

Rapid Estimation of the Ecological State of Coastal Water Areas Based on Shipboard Passive Remote Optical Sensing of the Water Surface

The study of the ecological state of coastal areas often requires rapid acquisition of detailed data. In this work, sea radiance coefficient spectra are analyzed, which were measured with a new three-channel passive optical complex for ecological monitoring of marine aquatoria (EMMA), developed by us, which operates semiautomatically on board a moving ship. The measurements were carried out near the Brazilian coast at the Rio Grande river mouth. The spectra are processed using an original technique which is based on intrinsic properties of the pure sea water absorption spectrum (WASM – water absorption step method) and has been modified for eutrophic Case II waters. This enables us to estimate the absorption indices of the suspended matter and colored organic matter. The comparison of these remote estimates with the estimates made from water samples taken at special stations shows their high correlation. The distributions of the suspended matter and colored organic matter are retrieved from remote measurement data and compared to the satellite imagery for the water area under study.

Method for estimating admixture content in seawater using operative spectrophotometry

The paper discusses spectra of the radiance coefficient of the sea surface measured in the open ocean and in coastal waters, and different kinds of these spectra corresponding to the water types are revealed. The focus is the method of measuring the radiance coefficient from a moving ship with a hyperspectral spectrophotometer. The results of studying a water area of Russia’s Black Sea coast at river mouths are presented. A new calibration method that can process measurement results taking into account the impact of cloudiness and wind has been proposed and tested. The concentrations of the main admixtures in natural seawater in the studied water area are estimated according to the obtained spectra; these estimates are compared to the results of direct analysis of water samples. It has been shown that the method of remote measurement of the sea radiance coefficient from on board a ship makes it possible to obtain operative maps of the spatial distribution of the main seawater admixtures.

Radiometric Characteristics of KOMPSAT-3 Multispectral Images Using the Spectra of Well-Known Surface Tarps

A vicarious calibration with reference to characterized surface tarps was conducted to determine the first radiometric characteristics of KOMPSAT-3. The 6S radiative transfer model was also used by inputting various initial parameters, such as the spectral response function of KOMPSAT-3, and atmospheric and geometric conditions. Moderate-Resolution Imaging Spectroradiometer atmospheric products, such as aerosol optical depth, precipitable water, and total ozone, were used as input parameters to interpret solar radiation reflection, scattering, and absorption effects. In the first field campaign, the radiometric coefficients from each of the spectral bands were estimated by calculating the predicted radiance at sensor level and the digital number (DN) of KOMPSAT-3 based on a linear least squares fit over a range of target reflectance levels. The second field campaign measurements were also used to upgrade the KOMPSAT-3 DNs to radiance coefficients. The root-mean-square error differences between simulated radiance and measured radiance during the second field campaign for “sensor-to-itself” calibration were 2.072 W/m 2 sr (blue), 6.80 W/m 2 sr (green), 7.512 W/m 2 sr (NIR), and 5.712 W/m 2 sr (red), respectively. This highlights that radiometric calibration with tarps is a reliable method. Furthermore, the gain ratio between the first and the second one was <; 5%, indicating reasonable radiometric calibration results. Additionally, cross-validation of KOMPSAT-3 with radiometrically well-calibrated Landsat-8 was performed over bright desert. Although the difference between the vicarious calibration with surface tarps and cross-validation with Landsat-8 was significant, reasonable results were obtained under close geometrical conditions, despite inherent vicarious calibration error.

Method for sea water absorption spectra estimation on the basis of shipboard passive remote sensing data and pure sea water properties

An original method for calibration of spectra of the seawater surface radiance coefficient measured from onboard a moving ship with a three-channel optical spectrophotometer is proposed. The method is based on some characteristics of pure sea water absorption. Using this method, the sea water absorption spectra can be retrieved. Results of processing measurements in the Russian coastal area of the Black Sea near river mouths are given. The efficiency of the calibration method for radiance spectra measurements under variable clouds and wind is shown. The concentrations of the main natural seawater admixtures have been estimated from the absorption spectra retrieved, and the estimates have been compared with contact measurements in water samples. It is shown that the method developed for sea water analysis, which includes remote shipboard measurements of the seawater brightness coefficient, calibration of the spectra, seawater absorption spectra retrieval, and estimation of the main seawater admixture concentrations, can be used for the study of shelf and inland seawater areas because it does not imply any correlation between phytoplankton, dissolved organic matter (yellow substance), and suspended matter concentrations.

Algorithm to retrieve the melt pond fraction and the spectral albedo of Arctic summer ice from satellite optical data

A new algorithm to retrieve characteristics (albedo and melt pond fraction) of summer ice in the Arctic from optical satellite data is described. In contrast to other algorithms this algorithm does not use a priori values of the spectral albedo of the sea-ice constituents (such as melt ponds, white ice etc.). Instead, it is based on an analytical solution for the reflection from sea ice surface. The algorithm includes the correction of the sought-for ice and ponds characteristics with the iterative procedure based on the Newton–Raphson method. Also, it accounts for the bi-directional reflection from the ice/snow surface, which is particularly important for Arctic regions where the sun is low. The algorithm includes an original procedure for the atmospheric correction, as well. This algorithm is implemented as computer code called Melt Pond Detector (MPD). The input to the current version of the MPD algorithm is the MERIS Level 1B data, including the radiance coefficients at ten wavelengths and the solar and observation angles (zenith and azimuth). Also, specific parameters describing surface and atmospheric state can be set in a configuration input file. The software output is the map of the melt ponds area fraction and the spectral albedo of sea-ice in HDF5 format. The numerical verification shows that the MPD algorithm provides more accurate results for the light ponds than for the dark ones. The spectral albedo is retrieved with high accuracy for any type of ice and ponds.

A ΠCP-02 field spectroradiometer for a 0.35- to 2.50- µm spectral region

A ΠCP-02 field spectroradiometer operating in 0.35- to 2.50- fum visible, near IR, and medium IR spectral ranges is described. The spectroradiometer is intended for measuring the absolute values of spectral radiance densities, radiation polarization patterns, and spectral radiance coefficients of studied objects.

Spectrometric estimation of the content of chlorophyll in plants subjected to anthropogenic action

Spectral methods for determining the content of chlorophyll in vegetation subjected to anthropogenic action are considered. The regularities in the changes in the spectral radiance coefficients of vegetation in certain intervals of the visible range are considered in relation to the degree of remoteness of the pollution source.

Using BRDF for radiance and luminance calculation

Correct representation of the phenomenon of reflection of visible radiation or thermal radiation is a necessary precondition for accurate modelling of luminous phenomena (visualization) and thermal phenomena (heat transfer). A full description of reflective properties of materials is included in BRDF 1 The term BRDF (i.e. bi-directional reflectance distribution function) is used chiefly in computer graphics; lighting engineering uses the concepts of radiance coefficient q e or luminance coefficient q v: where “e”-energetic, “v”-visible. 1 —difficult to apply in computer calculations. The article presents several BRDF models and for the most extended model (the one developed by Embrechts), a method of determination of optimum coefficients defining BRDF is proposed, based on empirical data. The article presents an example of visualization illustrating the effects of spread reflection, using the method presented.

An algorithm for determining the radiance reflected from the rough sea surface using MODIS-N satellite radiometer data

A new algorithm is suggested for determining the radiance B/sub r/(/spl theta/, /spl phi/) reflected from the rough sea surface. The knowledge of B/sub r/(/spl theta/, /spl phi/) is needed for excluding the reflected solar radiation from the signal at the space receiver. Information on the reflected radiance is also required when estimating the state of the sea surface from space. The information (on reflected radiance) is important for problems such as estimating the chlorophyll concentration in sea water. The suggested algorithm was constructed based on direct measurements of the radiance coefficient /spl rho/ published in V. G. Akimov ei al. (1993) and J. A Shaw et al. (1997). The experimental results show that the slope distribution of sea surface elements depends not only on the wind speed near the sea surface but also on the stability of the lower part of the marine atmospheric boundary layer. It is shown that the failure to account for this effect causes an error of /spl plusmn/30% when estimating B/sub r/(/spl theta/, /spl phi/).

Landscape Ecology and Diversity Patterns in the Seasonal Tropics from Landsat TM Imagery

We examine patterns of landscape diversity in the seasonal tropical forests of northeastern Guatemala with analyses of Landsat Thematic Mapper (TM) imagery. Our primary objective is to demonstrate that TM analyses, without extensive field data, provide valuable information on landscape diversity patterns to aid conservation and development plans. A principal components analyses indicates that the major source of variability at the scale of TM resolution (°30 m) is related to TM band 4 (TM4) radiance, and that the second and third most important sources are related to TM bands 5 and 7, respectively. Cluster analysis of TM4, TM5, and TM7 radiance produced six distinct land‐cover types, which follow a topographic gradient. Both TM radiance and the radiance coefficient of variation (CV) are significant in discriminating land‐cover types. The primary source of variability within upland forests is related to TM4, and the primary sources of variability within lowland swamps are related to TM5 and TM7. We infer from these results that green leaf biomass is the most important variable in discriminating between land‐cover types in the uplands, and that canopy closure and degree of senescence are the most important variables in the lowland swamps. We also examined patterns of landscape diversity reflected in three landscape indices: the number of land‐cover types (LCT), the Shannon‐Weaver index of landscape evenness (S‐W), and a topographic index (TI). The strongest correlations were found for TM4 radiance and TI (r = 0.94, n = 30, P &lt; 0.0001) and S‐W (r = ‐0.72, n = 30, P &lt; 0.0001), and between TM4 radiance CV and LCT (rs = 0.67, n = 30, P &lt; 0.0001). Thus, TM4 provides a good measure of landscape diversity. We found a perfect nonparametric correlation (rs = 1, n = 6) between TM4 radiance CV within a land cover type and the type's TI rank, which probably reflects increasing canopy heterogeneity between lowland swamps and upland forests. Finally, we demonstrate the potential of TM‐based land‐cover maps and diversity indices in designing and monitoring nature reserves.

Reconstruction of the spectrum of the radiance coefficient from measurements at fixed wavelengths

A method permitting the complete ensemble of characteristics to be reconstructed from a few selected characteristics is suggested. Finding sets of characteristics which ensure a minimum error of reconstruction, as well as the reconstruction procedure itself, requires the invoking of information on the convariance relationships between the characteristics. The method has been applied to determine the wavelengths, optimal for the reconstruction of spectra of sea surface radiance coefficients in the western tropical Atlantic.

ESTIMATES OF THE SENSITIVITY OF COMBINATIONS OF SPECTRAL RADIANCE COEFFICIENTS TO PROPERTIES OF THE VEGETATION COVER

A method is proposed for the calculation, based on the Goudriaan model, of estimates of various combinations of spectral radiance coefficients Pi which are optimal for interpretation of soil color and moisture, vegetation cover density, above-ground reserves of phytomass, and color and orientation of phytoelements. These estimates correspond rather closely with actual measurements obtained from the field. Translated from: Vestnik Moskovskogo Universiteta, geografiya, 1986, No. 4, pp. 75-79.

Bidirectional reflectance spectroscopy: 1. Theory

An approximate analytic solution to the radiative transfer equation describing the scattering of light from particulate surfaces is derived. Multiple scattering and mutual shadowing are taken into account. Analytic expressions for the following quantities are found: bidirectional reflectance, radiance factor, radiance coefficient, normal, hemispherical, Bond, and physical albedos, integral phase function, phase integral, and limb‐darkening profile. Scattering functions for mixtures can be calculated, as well as corrections for comparing experimental laboratory transmission or reflection spectra with observational planetary spectra. An expression for the scattering efficiency of an irregular particle large compared with the wavelength is derived. For closely spaced, nonopaque particles this efficiency is approximated by (1 + αDe)−l, where α is the true absorption coefficient and De is an effective particle diameter of the order of twice the mean particle size. For monomineralic surfaces it is shown that α = ( 1 − w)/wDe, where w is the single‐scattering albedo and can be determined from reflectance measurements of a powder, so that α may be calculated from reflectance. This theory should be useful for interpretations of reflectance spectroscopy of laboratory surfaces and photometry of solar system objects. From photometric observations of a body the following may be estimated: average single‐scattering albedo, average particle phase function, average macroscopic slope, and porosity.

Computer-controlled gonioreflectometer for the measurement of spectral reflection characteristics

A computer-controlled apparatus-the gonioreflectometer-is described, which was designed and manufactured at the Physikalisch-Technische Bundesanstalt. It enables the spectral radiance coefficient to be measured for all relevant angles of incidence and viewing. From basic considerations about the relationship between reflection characteristics it is shown that, e.g., the reflectance or the radiance factor for standardized geometries can be calculated from the measured radiance coefficient. This makes it required instrumentation for the calibration of reflection standards.

Remote sensing of natural formations from measurements of radiance coefficients

This paper is devoted to the consideration of some problems of remote sensing of natural formations using radiance coefficients in the narrow spectral invervals. The techniques for the determination of the most informative spectral intervals, as developed by the authors of the paper, are given and the results obtained are presented. The technique for obtaining the training sample of spectral radiance coefficients, with the help of a four-objective camera applied by the authors, is described. Some problems regarding the construction of a “universal” alphabet for classes of natural formations are discussed.

Results of spectrophotometric measurements of natural formations from the spacecraft “Soyuz-9” and investigations of environment from space

During the “Soyuz-9” flight, the reflection spectra of various natural formations have been obtained by means of the handheld spectrograph RSS-2. Making use of the literature data on the surface reflection spectra for sand and water, the parameters of the atmospheric transfer operator were computed. The spectra obtained from the high altitude observations was corrected to spectral reflectance values at the earth's surface and compared with the curves for spectral radiance coefficients of different types of natural formations according to E. L. Krinov's classification. Using the parameters of the atmospheric transfer operator, the curves for spectral radiance coefficients of different types of natural formations as expected from space observations (Krinov's classification) have been computed.

A quantitative examination of the LTE condition in the effluent of an atmospheric pressure argon plasma jet

A sensitive and relatively unambiguous experimental test for local thermodynamic equilibrium (LTE) has been carried out 3 mm from the orifice of an unconfined atmospheric-pressure argon plasma jet with a front electrode L/D ratio of about 3. It was assumed only that the plasma consisted of the four species, argon atoms, metastable argon atoms, electrons, and argon ions, in intimate mixture. The Kramers-Unsöld relation normalized by in situ use of an Olsen arc (a device taken to be in thermodynamic equilibrium) was used to determined from the continuum radiance coefficient the pointwise electron and hence argon ion concentration. The concentration of 19·22 eV excited argon ions was determined by absolute intensity measurement of the 4806·90 Å line. The ratio of the concentration of these excited emitters to the measured total ion population was used in the appropriate Boltzmann equation to obtain a unique and sensitively determined ion-excitation temperature parameter, T α. To demonstrate LTE, it remains only to show that the absolute populations of argon ions and of metastables, calculated by the well-known principles of statistical mechanics for temperature T α, are in agreement with those observed. Ion populations were determined as described above, and metastable populations inferred from those for the 1·78 eV excited metastable state which gives rise to the 6965·43 Å line. Finally, the ion excitation temperature profile was extrapolated in a reasonable way to the edge of the jet, and the theoretical heat flow was computed for a proportional velocity profile. Satisfactory agreement with measured heat flux was obtained.

Determination of a Radiance-Coefficient Profile from the Observed Asymmetric Radiance Distribution of an Optically Thin Radiating Medium

A hypothetical experiment involving cross spectrographs is described in which the determination of the radiance-coefficient distribution of a circular optically thin asymmetric radiating medium is treated with some rigor. It is then shown that one may start from normal data (i.e., a single mildly asymmetric radiance distribution) and with equal rigor determine a radiance coefficient profile through the flame. Furthermore, it is shown that the solution is surprisingly indifferent to choice of center for reasonable errors of judgment. For purposes of intercomparison a numerical measure of asymmetry is proposed and some mention is made of the numerical techniques employed by the authors which seem to be exceptionally stable.