Observational evidence of plane parallel model biases: Apparent dependence of cloud optical depth on solar zenith angle

1996 ◽  
Vol 101 (D1) ◽  
pp. 1621-1634 ◽  
Author(s):  
Norman G. Loeb ◽  
Roger Davies
Keyword(s):  
Optical Depth ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Observational Evidence ◽  
Parallel Model ◽  
Cloud Optical Depth ◽  
Plane Parallel ◽  
Model Biases

scholarly journals Simulating irradiance enhancement dependence on cloud optical depth and solar zenith angle

Solar Energy ◽  
2016 ◽  
Vol 136 ◽  
pp. 675-681 ◽  
Author(s):  
Zachary K. Pecenak ◽  
Felipe A. Mejia ◽  
Ben Kurtz ◽  
Amato Evan ◽  
Jan Kleissl
Keyword(s):  
Optical Depth ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Cloud Optical Depth

scholarly journals Liquid marine cloud geometric thickness retrieved from OCO-2's oxygen A-band spectrometer

2018 ◽  
Author(s):  
Mark Richardson ◽  
Jussi Leinonen ◽  
Heather Q. Cronk ◽  
James McDuffie ◽  
Matthew D. Lebsock ◽  
...  
Keyword(s):  
Optical Depth ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Single Layer ◽  
Satellite Observation ◽  
Retrieval Performance ◽  
Cloud Optical Depth ◽  
Cloud Top Pressure ◽  
Geometric Thickness

Abstract. This paper introduces the OCO2CLD-LIDAR-AUX product, which uses the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar and the Orbiting Carbon Observatory-2 (OCO-2) hyperspectral A-band spectrometer. CALIPSO provides a prior cloud top pressure (Ptop) for an OCO-2 based retrieval of cloud optical depth, Ptop and cloud geometric thickness expressed in hPa. Measurements are of single-layer liquid clouds over oceans from September 2014 to December 2016 when collocated data are available. Retrieval performance is best for solar zenith angle

scholarly journals Anthropogenic CO<sub>2</sub> monitoring satellite mission: the need for multi-angle polarimetric observations

2020 ◽  
Author(s):  
Stephanie P. Rusli ◽  
Otto Hasekamp ◽  
Joost aan de Brugh ◽  
Guangliang Fu ◽  
Yasjka Meijer ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Zenith Angle ◽  
Atmospheric Aerosols ◽  
Solar Zenith Angle ◽  
Added Value ◽  
Aerosol Layer ◽  
Satellite Mission ◽  
Measurement Uncertainties ◽  
Data Yield

Abstract. Atmospheric aerosols have been known to be a major source of uncertainties in CO2 concentrations retrieved from space. In this study, we investigate the added value of multi-angle polarimeter (MAP) measurements in the context of the Copernicus candidate mission for anthropogenic CO2 monitoring (CO2M). To this end, we compare aerosol-induced XCO2 errors from standard retrievals using spectrometer only (without MAP) with those from retrievals using both MAP and spectrometer. MAP observations are expected to provide information about aerosols that is useful for improving XCO2 accuracy. For the purpose of this work, we generate synthetic measurements for different atmospheric and geophysical scenes over land, based on which XCO2 retrieval errors are assessed. We show that the standard XCO2 retrieval approach that makes no use of auxiliary aerosol observations returns XCO2 errors with an overall bias of 1.12 ppm, and a spread (defined as half of the 15.9th to the 84.1th percentile range) of 2.07 ppm. The latter is far higher than the required XCO2 accuracy (0.5 ppm) and precision (0.7 ppm) of the CO2M mission. Moreover, these XCO2 errors exhibit a significantly larger bias and scatter at high aerosol optical depth, high aerosol altitude, and low solar zenith angle, which could lead to a worse performance in retrieving XCO2 from polluted areas where CO2 and aerosols are co-emitted. We proceed to determine MAP instrument specifications in terms of wavelength range, number of viewing angles, and measurement uncertainties that are required to achieve XCO2 accuracy and precision targets of the mission. Two different MAP instrument concepts are considered in this analysis. We find that for either concept, MAP measurement uncertainties on radiance and degree of linear polarization should be no more than 3 % and 0.003, respectively. Adopting the derived MAP requirements, a retrieval exercise using both MAP and spectrometer measurements of the synthetic scenes delivers XCO2 errors with an overall bias of −0.004 ppm and a spread of 0.54 ppm, implying compliance with the CO2M mission requirements; the very low bias is especially important for proper emission estimates. For the test ensemble, we find effectively no dependence of the XCO2 errors on aerosol optical depth, altitude of the aerosol layer, and solar zenith angle. These results indicate a major improvement in the retrieved XCO2 accuracy with respect to the standard retrieval approach, which could lead to a higher data yield, better global coverage, and a more comprehensive determination of CO2 sinks and sources. As such, this outcome underlines the contribution of, and therefore the need for, a MAP instrument onboard the CO2M mission.

scholarly journals A Parametric Radiative Forcing Model for Contrail Cirrus

2012 ◽  
Vol 51 (7) ◽  
pp. 1391-1406 ◽  
Author(s):  
U. Schumann ◽  
B. Mayer ◽  
K. Graf ◽  
H. Mannstein
Keyword(s):  
Analytical Model ◽  
Optical Depth ◽  
Zenith Angle ◽  
Radiative Forcing ◽  
Solar Zenith Angle ◽  
Life Cycles ◽  
Radiative Transfer Model ◽  
Model Parameters ◽  
Transfer Model ◽  
Wide Range

AbstractA new parameterized analytical model is presented to compute the instantaneous radiative forcing (RF) at the top of the atmosphere (TOA) produced by an additional thin contrail cirrus layer (called “contrail” below). The model calculates the RF using as input the outgoing longwave radiation and reflected solar radiation values at TOA for a contrail-free atmosphere, so that the model is applicable for both cloud-free and cloudy ambient atmospheres. Additional input includes the contrail temperature, contrail optical depth (at 550 nm), effective particle radius, particle habit, solar zenith angle, and the optical depth of cirrus above the contrail layer. The model parameters (5 for longwave and 10 for shortwave) are determined from least squares fits to calculations from the “libRadtran” radiative transfer model over a wide range of atmospheric and surface conditions. The correlation coefficient between model and calculations is larger than 98%. The analytical model is compared with published results, including a 1-yr simulation of global RF, and is found to agree well with previous studies. The fast analytical model is part of a larger modeling system to simulate contrail life cycles (“CoCiP”) and can allow for the rapid simulation of contrail cirrus RF over a wide range of meteorological conditions and for a given size-dependent habit mixture. Ambient clouds are shown to have large local impact on the net RF of contrails. Net RF of contrails may both increase and decrease and even change sign in the presence of higher-level cirrus, depending on solar zenith angle.

scholarly journals Coupling sky images with three-dimensional radiative transfer models: a new method to estimate cloud optical depth

2015 ◽  
Vol 8 (10) ◽  
pp. 11285-11321 ◽  
Author(s):  
F. A. Mejia ◽  
B. Kurtz ◽  
K. Murray ◽  
L. M. Hinkelman ◽  
M. Sengupta ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Optical Depth ◽  
Zenith Angle ◽  
Microwave Radiometer ◽  
Three Dimensional ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Cloud Detection ◽  
Cloud Optical Depth ◽  
Direct Normal Irradiance

Abstract. A method for retrieving cloud optical depth (τc) using a ground-based sky imager (USI) is presented. The Radiance Red-Blue Ratio (RRBR) method is motivated from the analysis of simulated images of various τc produced by a 3-D Radiative Transfer Model (3DRTM). From these images the basic parameters affecting the radiance and RBR of a pixel are identified as the solar zenith angle (θ0), τc, solar pixel angle/scattering angle (&amp;vartheta;s), and pixel zenith angle/view angle (&amp;vartheta;z). The effects of these parameters are described and the functions for radiance, Iλ(τc, θ0, &amp;vartheta;s, &amp;vartheta;z) and the red-blue ratio, RBR(τc, θ0, &amp;vartheta;s, &amp;vartheta;z) are retrieved from the 3DRTM results. RBR, which is commonly used for cloud detection in sky images, provides non-unique solutions for τc, where RBR increases with τc up to about τc = 1 (depending on other parameters) and then decreases. Therefore, the RRBR algorithm uses the measured Iλmeas(&amp;vartheta;s, &amp;vartheta;z), in addition to RBRmeas(&amp;vartheta;s, &amp;vartheta;z) to obtain a unique solution for τc. The RRBR method is applied to images taken by a USI at the Oklahoma Atmospheric Radiation Measurement program (ARM) site over the course of 220 days and validated against measurements from a microwave radiometer (MWR); output from the Min method for overcast skies, and τc retrieved by Beer's law from direct normal irradiance (DNI) measurements. A τc RMSE of 5.6 between the Min method and the USI are observed. The MWR and USI have an RMSE of 2.3 which is well within the uncertainty of the MWR. An RMSE of 0.95 between the USI and DNI retrieved τc is observed. The procedure developed here provides a foundation to test and develop other cloud detection algorithms.

scholarly journals Anthropogenic CO<sub>2</sub> monitoring satellite mission: the need for multi-angle polarimetric observations

2021 ◽  
Vol 14 (2) ◽  
pp. 1167-1190
Author(s):  
Stephanie P. Rusli ◽  
Otto Hasekamp ◽  
Joost aan de Brugh ◽  
Guangliang Fu ◽  
Yasjka Meijer ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Zenith Angle ◽  
Atmospheric Aerosols ◽  
Solar Zenith Angle ◽  
Added Value ◽  
Aerosol Layer ◽  
Satellite Mission ◽  
Measurement Uncertainties ◽  
Data Yield

Abstract. Atmospheric aerosols have been known to be a major source of uncertainties in CO2 concentrations retrieved from space. In this study, we investigate the added value of multi-angle polarimeter (MAP) measurements in the context of the Copernicus Anthropogenic Carbon Dioxide Monitoring (CO2M) mission. To this end, we compare aerosol-induced XCO2 errors from standard retrievals using a spectrometer only (without MAP) with those from retrievals using both MAP and a spectrometer. MAP observations are expected to provide information about aerosols that is useful for improving XCO2 accuracy. For the purpose of this work, we generate synthetic measurements for different atmospheric and geophysical scenes over land, based on which XCO2 retrieval errors are assessed. We show that the standard XCO2 retrieval approach that makes no use of auxiliary aerosol observations returns XCO2 errors with an overall bias of 1.12 ppm and a spread (defined as half of the 15.9–84.1 percentile range) of 2.07 ppm. The latter is far higher than the required XCO2 accuracy (0.5 ppm) and precision (0.7 ppm) of the CO2M mission. Moreover, these XCO2 errors exhibit a significantly larger bias and scatter at high aerosol optical depth, high aerosol altitude, and low solar zenith angle, which could lead to worse performance in retrieving XCO2 from polluted areas where CO2 and aerosols are co-emitted. We proceed to determine MAP instrument specifications in terms of wavelength range, number of viewing angles, and measurement uncertainties that are required to achieve XCO2 accuracy and precision targets of the mission. Two different MAP instrument concepts are considered in this analysis. We find that for either concept, MAP measurement uncertainties on radiance and degree of linear polarization should be no more than 3 % and 0.003, respectively. A retrieval exercise using MAP and spectrometer measurements of the synthetic scenes is carried out for each of the two MAP concepts. The resulting XCO2 errors have an overall bias of −0.004 ppm and a spread of 0.54 ppm for one concept, and a bias of 0.02 ppm and a spread of 0.52 ppm for the other concept. Both are compliant with the CO2M mission requirements; the very low bias is especially important for proper emission estimates. For the test ensemble, we find effectively no dependence of the XCO2 errors on aerosol optical depth, altitude of the aerosol layer, and solar zenith angle. These results indicate a major improvement in the retrieved XCO2 accuracy with respect to the standard retrieval approach, which could lead to a higher data yield, better global coverage, and a more comprehensive determination of CO2 sinks and sources. As such, this outcome underlines the contribution of, and therefore the need for, a MAP instrument aboard the CO2M mission.

An Efficient and Accurate Algorithm for Computing Grid-Averaged Solar Fluxes for Horizontally Inhomogeneous Clouds

2020 ◽  
Author(s):  
Zhonghai Jin ◽  
Andrew Lacis
Keyword(s):  
Optical Depth ◽  
Computational Time ◽  
Asymmetry Factor ◽  
Computationally Efficient ◽  
Transfer Scheme ◽  
Single Plane ◽  
Cloud Optical Depth ◽  
Plane Parallel ◽  
Special Cases ◽  
Time Required

AbstractA computationally efficient method is presented to account for the horizontal cloud inhomogeneity by using a radiatively equivalent plane parallel homogeneous (PPH) cloud. The algorithm can accurately match the calculations of the reference (rPPH) independent column approximation (ICA) results, but use only the same computational time required for a single plane parallel computation. The effective optical depth of this synthetic sPPH cloud is derived by exactly matching the direct transmission to that of the inhomogeneous ICA cloud. The effective scattering asymmetry factor is found from a pre-calculated albedo inverse look-up-table that is allowed to vary over the range from -1.0 to 1.0. In the special cases of conservative scattering and total absorption, the synthetic method is exactly equivalent to the ICA, with only a small bias (about 0.2% in flux) relative to ICA due to imperfect interpolation in using the look-up tables. In principlel, the ICA albedo can be approximated accurately regardless of cloud inhomogeneity. For a more complete comparison, the broadband shortwave albedo and transmission calculated from the synthetic sPPH cloud and averaged over all incident directions, have the RMS biases of 0.26% and 0.76%, respectively, for inhomogeneous clouds over a wide variation of particle size. The advantages of the synthetic PPH method are that (1) it is not required that all the cloud subcolumns have uniform microphysical characteristic, (2) it is applicable to any 1D radiative transfer scheme, and (3) it can handle arbitrary cloud optical depth distributions and an arbitrary number of cloud subcolumns with uniform computational efficiency.

Anthropogenic CO2 monitoring satellite mission: the need for multi-angle polarimetric observations

2020 ◽  
Author(s):  
Stephanie P. Rusli ◽  
Otto Hasekamp ◽  
Joost aan de Brugh ◽  
Guangliang Fu ◽  
Yasjka Meijer ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Zenith Angle ◽  
Linear Polarization ◽  
Solar Zenith Angle ◽  
Added Value ◽  
Aerosol Layer ◽  
Satellite Mission ◽  
Measurement Uncertainties ◽  
Data Yield

&lt;p&gt;Scattering due to aerosols and cirrus has long been identified as one of main sources of uncertainties in retrieving XCO&lt;sub&gt;2&lt;/sub&gt; from solar backscattered radiation. In this work, we investigate the added value of multi-angle polarimeter (MAP) measurements in the context of Copernicus candidate mission for anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; monitoring (CO2M). To this end, we compare aerosol-induced XCO&lt;sub&gt;2&lt;/sub&gt; errors from standard retrievals using spectrometer only (without MAP) with those from retrievals using both MAP and spectrometer. MAP measures radiance and degree of linear polarization (DLP) simultaneously at multiple wavelengths and at multiple viewing angles; these observations are expected to provide information about aerosols that is useful for improving XCO&lt;sub&gt;2&lt;/sub&gt; accuracy. Using an ensemble of 500 synthetic scenes over land, we show that the standard XCO&lt;sub&gt;2&lt;/sub&gt; retrieval approach that makes no use of MAP observations returns XCO&lt;sub&gt;2&lt;/sub&gt; errors with an overall bias of 1.04 ppm, and a spread (equivalent to standard deviation for a normal distribution) of 2.07 ppm. The latter is far higher than the required XCO&lt;sub&gt;2&lt;/sub&gt; accuracy (0.5 ppm) and precision (0.7 ppm) of the CO2M mission. Moreover, these XCO&lt;sub&gt;2&lt;/sub&gt; errors exhibit a significantly larger bias and scatter at high aerosol optical depth, high aerosol altitude, and low solar zenith angle, which suggest a worse performance in retrieving XCO&lt;sub&gt;2&lt;/sub&gt; from polluted areas where CO&lt;sub&gt;2&lt;/sub&gt; and aerosols are co-emitted. Given the CO2M mission requirements, we proceed to derive MAP instrument specifications in terms of measurement uncertainties, number of viewing angles, and the wavelength range. Two different MAP instrument concepts are considered in this requirement analysis. We find that for either concept, MAP measurement uncertainties on radiance and degree of linear polarization should be no more than 3% and 0.003, respectively. Adopting the derived MAP requirements, a retrieval exercise on the 500 synthetic scenes using both MAP and spectrometer measurements delivers XCO&lt;sub&gt;2&lt;/sub&gt; errors with an overall bias of -0.09 ppm and a spread of 0.57 ppm, indicating compliance with the CO2M mission requirements. For the test ensemble, we find effectively no dependence of the XCO&lt;sub&gt;2&lt;/sub&gt; errors on aerosol optical depth, altitude of the aerosol layer, and solar zenith angle. These results represent a significant improvement in the retrieved XCO&lt;sub&gt;2&lt;/sub&gt; accuracy compared to the standard retrieval approach, which may lead to a higher data yield, better global coverage, and a more comprehensive determination of CO&lt;sub&gt;2&lt;/sub&gt; sinks and sources. As such, this outcome underscores the contribution of, and therefore the need for, a MAP instrument onboard the CO2M mission.&lt;/p&gt;

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