Radiance

About: Radiance is a research topic. Over the lifetime, 9537 publications have been published within this topic receiving 215652 citations.

Passive remote sensing techniques for mapping water depth and bottom features.

Abstract: Ratio processing methods are reviewed, and a new method is proposed for extracting water depth and bottom type information from passive multispectral scanner data. Limitations of each technique are discussed, and an error analysis is performed using an analytical model for the radiance over shallow water.

Remote sensing of aerosol properties over oceans using the MODIS/EOS spectral radiances

Abstract: Spectral radiances measured at the top of the atmosphere in a wide spectral range (0.55–2.13 μm) are used to monitor the aerosol optical thickness and the aerosol size distribution (integrated on the vertical column) of the ambient (undisturbed) aerosol over the oceans. Even for the moderate resolution imaging spectrometer (MODIS) wide spectral range, only three parameters that describe the aerosol loading and size distribution can be retrieved. These three parameters are not always unique. For instance, the spectral radiance of an aerosol with a bilognormal size distribution can be simulated very well with a single lognormal aerosol with an appropriate mean radius and width of distribution. Preassumptions on the general structure of the size distribution are therefore required in the inversion of MODIS data. The retrieval of the aerosol properties is performed using lookup table computations. The volume size distribution in the lookup table is described with two lognormal modes: a single mode to describe the accumulation mode particles (radius 1.0 μm). Note that two accumulation modes may be present, one dominated by gas phase processes and a second dominated by cloud phase processes. The coarse mode can also be split into several partially overlapping modes describing maritime salt particles and dust. The aerosol parameters we expect to retrieve are η, the fractional contribution of the accumulation mode to scattering; τ, the spectral optical thickness; and rm, the mean particle size of the dominant mode. Additional radiative quantities such as asymmetry parameter and effective radius are derived subsequently. The impact of the surface conditions, wind speed and chlorophyll content on the retrieval is estimated, the impact of potential sources of error like the calibration of the instrument is also tested. The algorithm has been applied successfully to actual data sets provided by the Thematic Mapper on Landsat 5 and by the MODIS airborne simulator on the ER-2 and tested against ground and airborne measurements. A first estimate of the general accuracy is Δτ = ±0.05±0.05τ (at 550 nm), Δrm = 0.3rm, Δη = ±0.25.

Derivation of aerosol properties from satellite measurements of backscattered ultraviolet radiation: Theoretical basis

Abstract: We discuss the theoretical basis of a recently developed technique to characterize aerosols from space. We show that the interaction between aerosols and the strong molecular scattering in the near ultraviolet produces spectral variations of the backscattered radiances that can be used to separate aerosol absorption from scattering effects. This capability allows identification of several aerosol types, ranging from nonabsorbing sulfates to highly UV-absorbing mineral dust, over both land and water surfaces. Two ways of using the information contained in the near-UV radiances are discussed. In the first method, a residual quantity, which measures the departure of the observed spectral contrast from that of a molecular atmosphere, is computed. Since clouds yield nearly zero residues, this method is a useful way of separately mapping the spatial distribution of UV-absorbing and nonabsorbing particles. To convert the residue to optical depth, the aerosol type must be known. The second method is an inversion procedure that uses forward calculations of backscattered radiances for an ensemble of aerosol models. Using a look-up table approach, a set of measurements given by the ratio of backscattered radiance at 340-380 nm and the 380 nm radiance are associated, within the domain of the candidate aerosol models, to values of optical depth and single-scattering albedo. No previous knowledge of aerosol type is required. We present a sensitivity analysis of various error sources contributing to the estimation of aerosol properties by the two methods.

An improved method for detecting clear sky and cloudy radiances from AVHRR data

Abstract: To obtain accurate estimates of surface and cloud parameters from satellite radiance data a scheme has to be devised which identifies cloud-free and cloud-filled pixels (i.e. fields of view). Such a scheme has been developed for application to high resolution (1·1 km pixel) images recorded over Western Europe and the North Atlantic by the AVHRR on the TIROS-N/NOAA polar orbiters. The scheme consists of five daytime or five night-time tests applied to each individual pixel to determine whether that pixel is cloud-free, partly cloudy or cloud-filled. The pixel is only identified as cloud-free or cloud-filled if it passes all the tests to identify that condition; otherwise it is assumed to be partly cloudy. Surface parameters (e.g. skin temperature, reflectance, vegetation index, snow cover) can then be inferred from the cloud-free radiances, and cloud parameters (e.g. cloud top temperature, optical depth and liquid water content) from the cloud-filled radiances. Only fractional cloud cover is deriv...

Remote Sensing: The Image Chain Approach

Abstract: 1. Introduction 2. Historical Perspective and photo Mensuration 3. Radiometry and radiation Propagation 4. The Governing Equation for Radiance Reaching the Sensor 5. Sensors 6. Atmospheric Calibration - Solutions to the Governing Equation 7. Digital Imaging Processing for Image Exploitation 8. Information Dissemination 9. Weak Links in the Chain 10. Image Modeling