Uncertainties in cloud phase and optical thickness retrievals from the Earth Polychromatic Imaging Camera (EPIC)
TL;DR: Investigation of the expected uncertainties of a single channel cloud optical thickness (COT) retrieval technique, as well as a simple cloud temperature threshold based thermodynamic phase approach, in support of the Deep Space Climate Observatory (DSCOVR) mission show that a singleChannel COT retrieval is feasible for EPIC.
Abstract: . This paper presents an investigation of the expected uncertainties of a single-channel cloud optical thickness (COT) retrieval technique, as well as a simple cloud-temperature-threshold-based thermodynamic phase approach, in support of the Deep Space Climate Observatory (DSCOVR) mission. DSCOVR cloud products will be derived from Earth Polychromatic Imaging Camera (EPIC) observations in the ultraviolet and visible spectra. Since EPIC is not equipped with a spectral channel in the shortwave or mid-wave infrared that is sensitive to cloud effective radius (CER), COT will be inferred from a single visible channel with the assumption of appropriate CER values for liquid and ice phase clouds. One month of Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) daytime granules from April 2005 is selected for investigating cloud phase sensitivity, and a subset of these granules that has similar EPIC Sun-view geometry is selected for investigating COT uncertainties. EPIC COT retrievals are simulated with the same algorithm as the operational MODIS cloud products (MOD06), except using fixed phase-dependent CER values. Uncertainty estimates are derived by comparing the single-channel COT retrievals with the baseline bi-spectral MODIS retrievals. Results show that a single-channel COT retrieval is feasible for EPIC. For ice clouds, single-channel retrieval errors are minimal (
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TL;DR: The observation of horizontally oriented ice crystals in clouds and the unexpected use of the O2 B-band absorption for vegetation properties are described.
Abstract: The NOAA Deep Space Climate Observatory (DSCOVR) spacecraft was launched on February 11, 2015, and in June 2015 achieved its orbit at the first Lagrange point or L1, 1.5 million km from Earth towards the Sun. There are two NASA Earth observing instruments onboard: the Earth Polychromatic Imaging Camera (EPIC) and the National Institute of Standards and Technology Advanced Radiometer (NISTAR). The purpose of this paper is to describe various capabilities of the DSCOVR/EPIC instrument. EPIC views the entire sunlit Earth from sunrise to sunset at the backscattering direction (scattering angles between 168.5° and 175.5°) with 10 narrowband filters: 317, 325, 340, 388, 443, 552, 680, 688, 764 and 779 nm. We discuss a number of pre-processingsteps necessary for EPIC calibration including the geolocation algorithm and the radiometric calibration for each wavelength channel in terms of EPIC counts/second for conversion to reflectance units. The principal EPIC products are total ozone O3amount, scene reflectivity, erythemal irradiance, UV aerosol properties, sulfur dioxide SO2 for volcanic eruptions, surface spectral reflectance, vegetation properties, and cloud products including cloud height. Finally, we describe the observation of horizontally oriented ice crystals in clouds and the unexpected use of the O2 B-band absorption for vegetation properties.
116 citations
TL;DR: In this article, the authors used a random forest model to estimate global hourly downward shortwave radiation (SW) and photosynthetically active radiation (PAR) at 0.1°×0.0° (about 10 km at equator) spatial resolution based on EPIC measurements.
39 citations
TL;DR: Comparison with co-located cloud retrievals from geosynchronous earth orbit (GEO) and lowearth orbit (LEO) satellites shows that the EPIC cloud product algorithms are performing well and are consistent with theoretical expectations.
Abstract: . This paper presents the physical basis of the Earth Polychromatic Imaging
Camera (EPIC) cloud product algorithms and an initial evaluation of their
performance. Since June 2015, EPIC has been providing observations of the
sunlit side of the Earth with its 10 spectral channels ranging from the UV to
the near-infrared. A suite of algorithms has been developed to generate the
standard EPIC Level 2 cloud products that include cloud mask, cloud effective
pressure/height, and cloud optical thickness. The EPIC cloud mask adopts the
threshold method and utilizes multichannel observations and ratios as tests.
Cloud effective pressure/height is derived with observations from the
O2 A-band (780 and 764 nm) and B-band (680 and 688 nm) pairs. The
EPIC cloud optical thickness retrieval adopts a single-channel approach in
which the 780 and 680 nm channels are used for retrievals over ocean and
over land, respectively. Comparison with co-located cloud retrievals from
geosynchronous earth orbit (GEO) and low earth orbit (LEO) satellites shows
that the EPIC cloud product algorithms are performing well and are consistent
with theoretical expectations. These products are publicly available at the
Atmospheric Science Data Center at the NASA Langley Research Center for
climate studies and for generating other geophysical products that require
cloud properties as input.
31 citations
Cites background or methods from "Uncertainties in cloud phase and op..."
...A separate comprehensive 10 study has been conducted to investigate the feasibility and uncertainty of the EPIC COT retrieval algorithm (Meyer et al. 2016)....
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...…ancillary atmospheric profile, surface spectral reflectance, cloud forward model, and cloud effective radius assumptions, are provided in the current version of the operational products (Meyer et al., 2016, Platnick et al., 2017); uncertainty for other products will be included in the next version....
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...…atmospheric profile, surface spectral reflectance, cloud forward model, and cloud effective radius assumptions, are provided in the current version of the operational products (Meyer et al., 2016, Platnick et al., 2017); uncertainty for other products will be included in the next version.”...
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...Using MODIS data, it has been shown that the uncertainties for a single channel retrieval due to assuming a fixed cloud effective radius are roughly 10% for liquid clouds and 2% for ice clouds (Meyer et al. 2016)....
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...…and 147.5 hPa, respectively” For the COT retrieval, we have conducted a separate study on the uncertainty of using a one channel retrieval algorithm (Meyer et al. 2016) and the results are reiterated here: “for ice clouds, uncertainties are mostly less than 2%, because even though a fixed particle…...
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TL;DR: An overview of the algorithms and an evaluation of the intersensor continuity of the core CLDPROP_MODIS and CLD PROP_VIIRS cloud optical property datasets, i.e., cloud thermodynamic phase, optical thickness, effective particle size, and derived water path are presented.
Abstract: The NASA Aqua MODIS and Suomi National Polar-Orbiting Partnership (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) climate data record continuity cloud properties products (CLDPROP) were publicly released in April 2019 with an update later that year (Version 1.1). These cloud products, having heritage with the NASA Moderate-resolution Imaging Spectroradiometer (MODIS) MOD06 cloud optical properties product and the NOAA GOES-R Algorithm Working Group (AWG) Cloud Height Algorithm (ACHA), represent an effort to bridge the multispectral imager records of NASA’s Earth Observing System (EOS) and NOAA’s current generation of operational weather satellites to achieve a continuous, multi-decadal climate data record for clouds that can extend well into the 2030s. CLDPROP offers a “continuity of approach,” applying common algorithms and ancillary datasets to both MODIS and VIIRS, including utilizing only a subset of spectral channels available on both sensors to help mitigate instrument differences. The initial release of the CLDPROP_MODIS and CLDPROP_VIIRS data records spans the SNPP observational record (2012-present). Here, we present an overview of the algorithms and an evaluation of the intersensor continuity of the core CLDPROP_MODIS and CLDPROP_VIIRS cloud optical property datasets, i.e., cloud thermodynamic phase, optical thickness, effective particle size, and derived water path. The evaluation includes analyses of pixel-level MODIS/VIIRS co-locations as well as spatial and temporal aggregated statistics, with a focus on identifying and understanding the root causes of individual dataset discontinuities. The results of this evaluation will inform future updates to the CLDPROP products and help scientific users determine the appropriate use of the product datasets for their specific needs.
24 citations
References
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TL;DR: The Modern-Era Retrospective Analysis for Research and Applications (MERRA) was undertaken by NASA's Global Modeling and Assimilation Office with two primary objectives: to place observations from NASA's Earth Observing System satellites into a climate context and to improve upon the hydrologic cycle represented in earlier generations of reanalyses as mentioned in this paper.
Abstract: The Modern-Era Retrospective Analysis for Research and Applications (MERRA) was undertaken by NASA’s Global Modeling and Assimilation Office with two primary objectives: to place observations from NASA’s Earth Observing System satellites into a climate context and to improve upon the hydrologic cycle represented in earlier generations of reanalyses. Focusing on the satellite era, from 1979 to the present, MERRA has achieved its goals with significant improvements in precipitation and water vapor climatology. Here, a brief overview of the system and some aspects of its performance, including quality assessment diagnostics from innovation and residual statistics, is given.By comparing MERRA with other updated reanalyses [the interim version of the next ECMWF Re-Analysis (ERA-Interim) and the Climate Forecast System Reanalysis (CFSR)], advances made in this new generation of reanalyses, as well as remaining deficiencies, are identified. Although there is little difference between the new reanalyses i...
4,572 citations
TL;DR: An advanced, thoroughly documented, and quite general purpose discrete ordinate algorithm for time-independent transfer calculations in vertically inhomogeneous, nonisothermal, plane-parallel media for Atmospheric applications ranging from the UV to the radar region of the electromagnetic spectrum is summarized.
Abstract: The transfer of monochromatic radiation in a scattering, absorbing, and emitting plane-parallel medium with a specified bidirectional reflectivity at the lower boundary is considered. The equations and boundary conditions are summarized. The numerical implementation of the theory is discussed with attention given to the reliable and efficient computation of eigenvalues and eigenvectors. Ways of avoiding fatal overflows and ill-conditioning in the matrix inversion needed to determine the integration constants are also presented.
3,257 citations
"Uncertainties in cloud phase and op..." refers methods in this paper
...The forward-calculated COT retrieval LUTs will be generated under assumptions and cloud models identical to those of MOD06 using the 1-D plane-parallel DIScreteOrdinates Radiative Transfer (DISORT) method (Stamnes et al., 1988) ignoring atmospheric gaseous absorption, which is corrected for during the retrieval process; note that abovecloud Rayleigh scattering, expected to be non-negligible at 680 nm, will also be accounted for during the retrieval process on a pixel-by-pixel basis using the iterative technique of Wang and King (1997), similar to MOD06....
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...…under assumptions and cloud models identical to those of MOD06 using the 1D plane-parallel DIScrete-Ordinates Radiative Transfer 5 (DISORT) method (Stamnes et al., 1988) ignoring atmospheric gaseous absorption, which is corrected for during the retrieval process; note that above-cloud Rayleigh…...
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TL;DR: In this paper, a method was developed for interpreting the statistics of the sun's glitter on the sea surface in terms of the statistic of the slope distribution, which was applied to aerial photographs taken under carefully chosen conditions in the Hawaiian area.
Abstract: A method is developed for interpreting the statistics of the sun’s glitter on the sea surface in terms of the statistics of the slope distribution. The method consists of two principal phases: (1) of identifying, from geometric considerations, any point on the surface with the particular slope required for the reflection of the” sun’s rays toward the observer; and (2) of interpreting the average brightness of the sea surface in the vicinity of this point in terms of the frequency with which this particular slope occurs. The computation of the probability of large (and infrequent) slopes is limited by the disappearance of the glitter into a background consisting of (1) the sunlight scattered from particles beneath the sea surface, and (2) the skylight reflected by the sea surface.The method has been applied to aerial photographs taken under carefully chosen conditions in the Hawaiian area. Winds were measured from a vessel at the time and place of the aerial photographs, and cover a range from 1 to 14 m sec−1. The effect of surface slicks, laid by the vessel, are included in the study. A two-dimensional Gram-Charlier series is fitted to the data. As a first approximation the distribution is Gaussian and isotropic with respect to direction. The mean square slope (regardless of direction) increases linearly with the wind speed, reaching a value of (tan16°)2 for a wind speed of 14 m sec−1. The ratio of the up/ downwind to the crosswind component of mean square slope varies from 1.0 to 1.9. There is some up/downwind skewness which increases with increasing wind speed. As a result the most probable slope at high winds is not zero but a few degrees, with the azimuth of ascent pointing downwind. The measured peakedness which is barely above the limit of observational error, is such as to make the probability of very large and very small slopes greater than Gaussian. The effect of oil slicks covering an area of one-quarter square mile is to reduce the mean square slopes by a factor of two or three, to eliminate skewness, but to leave peakedness unchanged.
2,270 citations
"Uncertainties in cloud phase and op..." refers background in this paper
...…relevant to EPIC include new bulk ice cloud radiative models (Yang et al., 2013), improved characterization of surface reflectance for ocean (Cox and Munk, 1954a,b) and land (Schaaf et al., 2011), new cloud radiative transfer (RT) look-up tables (LUTs), and improved handling of ancillary…...
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TL;DR: The progress report on the International Satellite Cloud Climatology Project (ISCCP) describes changes made to produce new cloud data products (D data), examines the evidence that these changes are improvements over the previous version (C data), summarizes some results, and discusses plans for the ISCCP through 2005.
Abstract: This progress report on the International Satellite Cloud Climatology Project (ISCCP) describes changes made to produce new cloud data products (D data), examines the evidence that these changes are improvements over the previous version (C data), summarizes some results, and discusses plans for the ISCCP through 2005. By late 1999 all datasets will be available for the period from July 1983 through December 1997. The most significant changes in the new D-series cloud datasets are 1) revised radiance calibrations to remove spurious changes in the long-term record, 2) increased cirrus detection sensitivity over land, 3) increased low-level cloud detection sensitivity in polar regions, 4) reduced biases in cirrus cloud properties using an ice crystal microphysics model in place of a liquid droplet microphysics model, and 5) increased detail about the variations of cloud properties. The ISCCP calibrations are now the most complete and self-consistent set of calibrations available for all the weather...
2,143 citations
"Uncertainties in cloud phase and op..." refers methods in this paper
...The 35 DSCOVR cloud products will be derived from EPIC observations in the ultraviolet and visible spectra, with cloud optical property retrieval heritage from ISCCP and the operational MODIS cloud products (MOD06)....
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...However, because the EPIC spectral channels do not extend to wavelengths longer than the NIR, COT retrievals will be performed using a single-channel approach similar to that of the International Satellite Cloud Climatology Project (ISCCP) (Rossow and Schiffer, 1999) and the Multi-angle Imaging 35 SpectroRadiometer (MISR) mission (Marchand et al., 2010), both of which assume appropriate values for CER....
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...…COT retrievals will be performed using a single-channel approach similar to that of the International Satellite Cloud Climatology Project (ISCCP) (Rossow and Schiffer, 1999) and the Multi-angle Imaging 35 SpectroRadiometer (MISR) mission (Marchand et al., 2010), both of which assume appropriate…...
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TL;DR: The various algorithms being used for the remote sensing of cloud properties from MODIS data with an emphasis on the pixel-level retrievals (referred to as Level-2 products), with 1-km or 5-km spatial resolution at nadir are described.
Abstract: The Moderate Resolution Imaging Spectroradiometer (MODIS) is one of five instruments aboard the Terra Earth Observing System (EOS) platform launched in December 1999. After achieving final orbit, MODIS began Earth observations in late February 2000 and has been acquiring data since that time. The instrument is also being flown on the Aqua spacecraft, launched in May 2002. A comprehensive set of remote sensing algorithms for cloud detection and the retrieval of cloud physical and optical properties have been developed by members of the MODIS atmosphere science team. The archived products from these algorithms have applications in climate change studies, climate modeling, numerical weather prediction, as well as fundamental atmospheric research. In addition to an extensive cloud mask, products include cloud-top properties (temperature, pressure, effective emissivity), cloud thermodynamic phase, cloud optical and microphysical parameters (optical thickness, effective particle radius, water path), as well as derived statistics. We will describe the various algorithms being used for the remote sensing of cloud properties from MODIS data with an emphasis on the pixel-level retrievals (referred to as Level-2 products), with 1-km or 5-km spatial resolution at nadir. An example of each Level-2 cloud product from a common data granule (5 min of data) off the coast of South America will be discussed. Future efforts will also be mentioned. Relevant points related to the global gridded statistics products (Level-3) are highlighted though additional details are given in an accompanying paper in this issue.
1,636 citations