On the Dependence of Discrete Ordinates Models for Layer Reflectance and Transmittance on Relative Optical Depth and Solar Zenith Angle

2009 ◽  
Vol 42 (1) ◽  
pp. 23-37 ◽  
Author(s):  
Marcos Pimenta de Abreu
Keyword(s):  
Optical Depth ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Discrete Ordinates

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 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.

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;

scholarly journals Rethinking the correction for absorbing aerosols in the satellite-based surface UV products

2021 ◽  
Author(s):  
Antti Arola ◽  
William Wandji Nyamsi ◽  
Antti Lipponen ◽  
Stelios Kazadzis ◽  
Nickolay A. Krotkov ◽  
...  
Keyword(s):  
Optical Depth ◽  
Uv Radiation ◽  
Correction Factor ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Retrieval Algorithm ◽  
Angle Dependence ◽  
Aerosol Absorption ◽  
Uv Irradiance ◽  
Absorbing Aerosols

Abstract. Satellite estimates of surface UV irradiance have been available since 1978 from TOMS UV spectrometer and continued with significantly improved ground resolution using Ozone Monitoring Instrument (OMI 2004-current) and Sentinel 5 Precursor (S5P 2017-current). The surface UV retrieval algorithm remains essentially the same: it first estimates the clear-sky UV irradiance based on measured ozone and then accounts for the attenuation by clouds and aerosols applying two consecutive correction factors. When estimating the total aerosol effect in surface UV irradiance, there are two major classes of aerosols to be considered: 1) aerosols that only scatter UV radiation and 2) aerosols that both scatter and absorb UV radiation. The former effect is implicitly included in the measured effective Lambertian Equivalent scene reflectivity (LER), so the scattering aerosol influence is estimated through cloud correction factor. Aerosols that absorb UV radiation attenuate the surface UV radiation more strongly than non-absorbing aerosols of the same extinction optical depth (AOD). Moreover, since these aerosols also attenuate the outgoing satellite-measured radiance, the cloud correction factor that treats these aerosols as purely scattering underestimates their AOD causing underestimation of LER and overestimation of surface UV irradiance. Therefore, for correction of aerosol absorption additional information is needed, such as the UV absorbing Aerosol Index (UVAI) or a model-based monthly climatology of aerosol absorption optical depth (AAOD). A correction for absorbing aerosols was proposed almost a decade ago and later implemented in the operational OMI and TROPOMI UV algorithms. In this study, however, we show that there is still room for an improvement to better account for the solar zenith angle dependence and non-linearity in the absorbing aerosol attenuation and as a result we propose an improved correction scheme. There are two main differences between the new proposed correction and the one that is currently operational in OMI and TROPOMI UV-algorithms. First, the currently operational correction for absorbing aerosols is a function of AAOD only, while the new correction takes additionally the solar zenith angle dependence into account. Second, the 2nd order polynomial of the new correction takes better into account the non-linearity in the correction as a function of AAOD, if compared to the currently operational one, and thus better describes the effect by absorbing aerosols over larger range of AAOD. To illustrate the potential impact of the new correction in the global UV estimates, we applied the current and new proposed correction for global fields of AAOD from the aerosol climatology currently used in OMI UV algorithm, showing a typical differences of ±5 %. This new correction is easy to implement operationally using information of solar zenith angle and existing AAOD climatology.

scholarly journals Rethinking the correction for absorbing aerosols in the OMI- and TROPOMI-like surface UV algorithms

2021 ◽  
Vol 14 (7) ◽  
pp. 4947-4957
Author(s):  
Antti Arola ◽  
William Wandji Nyamsi ◽  
Antti Lipponen ◽  
Stelios Kazadzis ◽  
Nickolay A. Krotkov ◽  
...  
Keyword(s):  
Optical Depth ◽  
Uv Radiation ◽  
Correction Factor ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Retrieval Algorithm ◽  
Ozone Monitoring Instrument ◽  
Aerosol Absorption ◽  
Uv Irradiance ◽  
Absorbing Aerosols

Abstract. Satellite estimates of surface UV irradiance have been available since 1978 from the TOMS UV spectrometer and have continued with significantly improved ground resolution using the Ozone Monitoring Instrument (OMI 2004–current) and Sentinel 5 Precursor (S5P 2017–current). The surface UV retrieval algorithm remains essentially the same: it first estimates the clear-sky UV irradiance based on measured ozone and then accounts for the attenuation by clouds and aerosols, applying two consecutive correction factors. When estimating the total aerosol effect in surface UV irradiance, there are two major classes of aerosols to be considered: (1) aerosols that only scatter UV radiation and (2) aerosols that both scatter and absorb UV radiation. The former effect is implicitly included in the measured effective Lambertian-equivalent scene reflectivity (LER), so the scattering aerosol influence is estimated through cloud correction factor. Aerosols that absorb UV radiation attenuate the surface UV radiation more strongly than non-absorbing aerosols of the same extinction optical depth. Moreover, since these aerosols also attenuate the outgoing satellite-measured radiance, the cloud correction factor that treats these aerosols as purely scattering underestimates their aerosol optical depth (AOD), causing underestimation of LER and overestimation of surface UV irradiance. Therefore, for correction of aerosol absorption, additional information is needed, such as a model-based monthly climatology of aerosol absorption optical depth (AAOD). A correction for absorbing aerosols was proposed almost a decade ago and later implemented in the operational OMI and TROPOMI UV algorithms. In this study, however, we show that there is still room for improvement to better account for the solar zenith angle (SZA) dependence and nonlinearity in the absorbing aerosol attenuation, and as a result we propose an improved correction scheme. There are two main differences between the new proposed correction and the one that is currently operational in OMI and TROPOMI UV algorithms. First, the currently operational correction for absorbing aerosols is a function of AAOD only, while the new correction additionally takes the solar zenith angle dependence into account. Second, the second-order polynomial of the new correction takes the nonlinearity in the correction as a function of AAOD better into account, if compared to the currently operational one, and thus better describes the effect by absorbing aerosols over a larger range of AAOD. To illustrate the potential impact of the new correction in the global UV estimates, we applied the current and new proposed correction for global fields of AAOD from the aerosol climatology currently used in OMI UV algorithm, showing a typical differences of ±5 %. This new correction is easy to implement operationally using information of solar zenith angle and existing AAOD climatology.

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 Downward surface flux computations in a vertically inhomogeneous grey planetary atmosphere

2008 ◽  
Vol 23 (1) ◽  
pp. 35-40
Author(s):  
Marcos Pimenta de Abreu
Keyword(s):  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Surface Flux ◽  
Model Atmosphere ◽  
Planetary Atmosphere ◽  
Surface Fluxes ◽  
Computational Scheme ◽  
Discrete Ordinates ◽  
Nodal Method ◽  
Efficient Scheme

We describe an efficient computational scheme for downward surface flux computations in a vertically inhomogeneous grey planetary atmosphere for different values of solar zenith angle. We start with the basic equations of a recently developed discrete ordinates spectral nodal method, and we derive suitable bidirectional functions whose diffuse components do not depend on the solar zenith angle. We then make use of these bidirectional functions to construct an efficient scheme for computing the downward surface fluxes in a given model atmosphere for a number of solar zenith angles. We illustrate the merit of the computational scheme described here with downward surface flux computations in a three-layer grey model atmosphere for four values of solar zenith angle, and we conclude this article with general remarks and directions for future work.

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