Results 1 - 10
of
225
Synergistic algorithm for estimating vegetation canopy leaf area index and fraction of absorbed photosynthetically active radiation from MODIS and MISR data
, 1998
"... A synergistic algorithm for producing global leaf area index and fraction of absorbed photosynthetically active radiation fields from canopy reflectance data measured by MODIS (moderate resolution imaging spectroradiometer) and MISR (multiangle imaging spectroradiometer) instruments aboard the EO ..."
Abstract
-
Cited by 177 (48 self)
- Add to MetaCart
A synergistic algorithm for producing global leaf area index and fraction of absorbed photosynthetically active radiation fields from canopy reflectance data measured by MODIS (moderate resolution imaging spectroradiometer) and MISR (multiangle imaging spectroradiometer) instruments aboard the EOS-AM 1 platform is described here. The proposed algorithm is based on a three-dimensional formulation of the radiative transfer process in vegetation canopies. It allows the use of information provided by MODIS (single angle and up to 7 shortwave spectral bands) and MISR (nine angles and four shortwave spectral bands) instruments within one algorithm. By accounting features specific to the problem of radiative transfer in plant canopies, powerful techniques developed in reactor theory and atmospheric physics are adapted to split a complicated three-dimensional radiative transfer problem into two independent, simpler subproblems, the solutions of which are stored in the form of a look-up table. The theoretical background required for the design of the synergistic algorithm is discussed.
Narrowband to broadband conversions of land surface albedo: I. Algorithms
- REMOTE SENSING OF THE ENVIRONMENT
, 2000
"... Land surface broadband albedo is a critical variable for many scientific applications. High-resolution narrowband satellite observations contain important information that enables us to map land surface albedo globally, and validate the coarse-resolution albedo products from the broadband sensors us ..."
Abstract
-
Cited by 83 (9 self)
- Add to MetaCart
(Show Context)
Land surface broadband albedo is a critical variable for many scientific applications. High-resolution narrowband satellite observations contain important information that enables us to map land surface albedo globally, and validate the coarse-resolution albedo products from the broadband sensors using ground ``point/plot' ' measurements. However, the conversions from narrowband to broadband albedos of a general surface type have not been well established. Most studies compute total shortwave albedo based on either the empirical relations between surface total shortwave albedo measurements and satellite observations or radiative transfer simulations with the limited number of surface reflectance spectra because of the computational constraints. As a result, many conversion formulae for the same sensors are quite different. In this study, we applied an approach that decouples surface reflectance spectra from the real-time radiative transfer simulations so that many different surface reflectance spectra and the atmospheric conditions can be effectively incorporated. The conversion formulae, based on extensive radiative transfer simulations, are provided in this paper for calculating the total shortwave albedo, total-, direct-, and diffuse-visible, and near-infrared broadband albedos for several narrowband sensors, including ASTER,
Does independent component analysis play a role in unmixing hyperspectral data
- IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING
, 2005
"... Independent component analysis (ICA) has recently been proposed as a tool to unmix hyperspectral data. ICA is founded on two assumptions: 1) the observed spectrum vector is a linear mixture of the constituent spectra (endmember spectra) weighted by the correspondent abundance fractions (sources); 2) ..."
Abstract
-
Cited by 61 (13 self)
- Add to MetaCart
Independent component analysis (ICA) has recently been proposed as a tool to unmix hyperspectral data. ICA is founded on two assumptions: 1) the observed spectrum vector is a linear mixture of the constituent spectra (endmember spectra) weighted by the correspondent abundance fractions (sources); 2) sources are statistically independent. Independent factor analysis (IFA) extends ICA to linear mixtures of independent sources immersed in noise. Concerning hyperspectral data, the first assumption is valid whenever the multiple scattering among the distinct constituent substances (endmembers) is negligible, and the surface is partitioned according to the fractional abundances. The second assumption, however, is violated, since the sum of abundance fractions associated to each pixel is constant due to physical constraints in the data acquisition process. Thus, sources cannot be statistically independent, this compromising the performance of ICA/IFA algorithms in hyperspectral unmixing. This paper studies the impact of hyperspectral source statistical dependence on ICA and IFA performances. We conclude that the accuracy of these methods tends to improve with the increase of the signature variability, of the number of endmembers, and of the signal-to-noise ratio. In any case, there are always endmembers incorrectly unmixed. We arrive to this conclusion by minimizing the mutual information of simulated and real hyperspectral mixtures. The computation of mutual information is based on fitting mixtures of Gaussians to the observed data. A method to sort ICA and IFA estimates in terms of the likelihood of being correctly unmixed is proposed.
Atmospheric correction of Landsat ETM+ land surface imagery – Part II: Validation and applications
- IEEE Transactions on Geoscience and Remote Sensing
, 2002
"... Abstract—To extract quantitative information from the En-hanced Thematic Mapper-Plus (ETM+) imagery accurately, atmospheric correction is a necessary step. After reviewing histor-ical development of atmospheric correction of Landsat thematic mapper (TM) imagery, we present a new algorithm that can e ..."
Abstract
-
Cited by 42 (8 self)
- Add to MetaCart
(Show Context)
Abstract—To extract quantitative information from the En-hanced Thematic Mapper-Plus (ETM+) imagery accurately, atmospheric correction is a necessary step. After reviewing histor-ical development of atmospheric correction of Landsat thematic mapper (TM) imagery, we present a new algorithm that can effec-tively estimate the spatial distribution of atmospheric aerosols and retrieve surface reflectance from ETM+ imagery under general atmospheric and surface conditions. This algorithm is therefore suitable for operational applications. A new formula that accounts for adjacency effects is also presented. Several examples are given to demonstrate that this new algorithm works very well under a variety of atmospheric and surface conditions. The companion paper will validate this method using ground measurements, and illustrate the improvements of several applications due to atmospheric correction. Index Terms—Adjacency effect, aerosol, atmospheric correc-tion, land surface, reflectance. I.
Inverse transport theory and applications
- Inverse Problems
"... Abstract. Inverse transport consists of reconstructing the optical properties of a domain from measurements performed at the domain’s boundary. This paper concerns several types of measurements: time dependent, time independent, angularly resolved and angularly averaged measurements. We review recen ..."
Abstract
-
Cited by 32 (8 self)
- Add to MetaCart
(Show Context)
Abstract. Inverse transport consists of reconstructing the optical properties of a domain from measurements performed at the domain’s boundary. This paper concerns several types of measurements: time dependent, time independent, angularly resolved and angularly averaged measurements. We review recent results on the reconstruction of the optical parameters from such measurements and the stability of such reconstructions. Inverse transport finds applications e.g. in medical imaging (optical tomography, optical molecular imaging) and in geophysical imaging (remote sensing in the Earth atmosphere).
A Delta-Eddington Multiple Scattering Parameterization for Solar Radiation
- in the Sea Ice Component of the Community Climate System Model, Ncar Tech. Note NCAR/TN-472+STR
, 2007
"... i TABLE OF CONTENTS Abstract................................ v ..."
Abstract
-
Cited by 24 (1 self)
- Add to MetaCart
(Show Context)
i TABLE OF CONTENTS Abstract................................ v
Intercomparison of models representing direct shortwave radiative forcing by sulfate aerosols
- J. Geophys. Res
, 1998
"... Abstract. The importance of aerosols as agents of climate change has recently been highlighted. However, the magnitude of aerosol forcing by scattering of shortwave radiation (direct forcing) is still very uncertain even for the relatively well characterized sulfate aerosol. A potential source of un ..."
Abstract
-
Cited by 21 (2 self)
- Add to MetaCart
Abstract. The importance of aerosols as agents of climate change has recently been highlighted. However, the magnitude of aerosol forcing by scattering of shortwave radiation (direct forcing) is still very uncertain even for the relatively well characterized sulfate aerosol. A potential source of uncertainty is in the model representation of aerosol optical properties and aerosol influences on radiative transfer in the atmosphere. Although radiative transfer methods and codes have been compared in the past, these comparisons have not focused on aerosol forcing (change in net radiative flux at the top of the atmosphere). Here we report results of a project involving 12 groups using 15 models to examine radiative forcing by sulfate aerosol for a wide range of values of particle radius, aerosol optical depth, surface albedo, and solar zenith angle. Among the models that were employed were high and low spectral resolution models incorporating a variety of radiative transfer approximations as well as a line-by-line model. The normalized forcings (forcing per sulfate column burden) obtained with the several radiative transfer models were examined, and the discrepancies were characterized. All models simulate forcings of comparable amplitude and exhibit a similar dependence on input parameters. As expected for a non-light-absorbing aerosol,
Validation of a vector version of the 6S radiative transfer code for atmospheric correction of satellite data. Part I: path radiance
- Appl. Opt
, 2006
"... is the second part of the validation effort of the recently developed vector version of the 6S (Second Simulation of a Satellite Signal in the Solar Spectrum) radiative transfer code (6SV1), primarily used for the calculation of look-up tables in the Moderate Resolution Imaging Spectroradiometer (MO ..."
Abstract
-
Cited by 19 (2 self)
- Add to MetaCart
(Show Context)
is the second part of the validation effort of the recently developed vector version of the 6S (Second Simulation of a Satellite Signal in the Solar Spectrum) radiative transfer code (6SV1), primarily used for the calculation of look-up tables in the Moderate Resolution Imaging Spectroradiometer (MODIS) atmo-spheric correction algorithm. The 6SV1 code was tested against a Monte Carlo code and Coulson’s tabulated values for molecular and aerosol atmospheres bounded by different Lambertian and anisotropic surfaces. The code was also tested in scalar mode against the scalar code SHARM to resolve the previous 6S accuracy issues in the case of an anisotropic surface. All test cases were characterized by good agreement between the 6SV1 and the other codes: The overall relative error did not exceed 0.8%. The study also showed that ignoring the effects of radiation polarization in the atmosphere led to large errors in the simulated top-of-atmosphere reflectances: The maximum observed error was approximately 7.2% for both Lambertian and anisotropic surfaces. © 2007 Optical Society of America OCIS codes: 280.1310, 290.4210, 010.1300, 010.1310, 010.1320, 120.0280. 1.
Well-Posedness And Convergence Of Some Regularization Methods For Nonlinear Ill-Posed Problems
- Inverse Problems
, 1989
"... : In this paper we carry out a theoretical analysis of two regularization methods for nonlinear ill-posed problems. The first is a penalty method called Tikhonov regularization, in which one solves an unconstrained optimization problem while the second is based on a constrained optimization problem. ..."
Abstract
-
Cited by 14 (2 self)
- Add to MetaCart
: In this paper we carry out a theoretical analysis of two regularization methods for nonlinear ill-posed problems. The first is a penalty method called Tikhonov regularization, in which one solves an unconstrained optimization problem while the second is based on a constrained optimization problem. For each method we examine the well-posedness of the respective optimization problem. We then show strong convergence of the regularized `solutions' to the true solution. (Note that this is well known for the application of these methods to linear problems.) In this analysis we consider such factors as the convergence of perturbed data to the true data, inexact solution of the respective optimization problems, and the choice of the regularization parameters. Key words: ill-posed, regularization, convergence, approximation 1 This joint research was done during the authors' visit to the Centre for Mathematical Analysis at the Australian National University, Canberra, Australia, with support ...
A direct algorithm for estimating land surface broadband albedos from MODIS imagery
- IEEE Trans. Geosci. Remote Sens
, 2003
"... Abstract—Land surface albedo is a critical variable needed in land surface modeling. The conventional methods for estimating broadband albedos rely on a series of steps in the processing chain, including atmospheric correction, surface angular modeling, and narrowband-to-broadband albedo conversions ..."
Abstract
-
Cited by 12 (8 self)
- Add to MetaCart
(Show Context)
Abstract—Land surface albedo is a critical variable needed in land surface modeling. The conventional methods for estimating broadband albedos rely on a series of steps in the processing chain, including atmospheric correction, surface angular modeling, and narrowband-to-broadband albedo conversions. Unfortunately, errors associated with each procedure may be accumulated and significantly impact the accuracy of the final albedo products. In an earlier study, we developed a new direct procedure that links the top-of-atmosphere spectral albedos with land surface broadband albedos without performing atmospheric correction and other processes. In this paper, this method is further improved in several aspects and implemented using actual Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. Several case studies indicated that this new method can predict land surface broadband albedos very accurately and eliminate aerosol effects effectively. It is very promising for global applications and is particularly suitable for nonvegetated land surfaces. Note that a Lambertian surface has been assumed in the radiative transfer simulation in this paper as a first-order approximation; this assumption can be easily removed as long as a global bidirectional reflectance distribution function climatology is available. Index Terms—Broadband albedo, land surface, MODIS, multispectral imagery, remote sensing.
