scholarly journals Development of on-site self-calibration and retrieval methods for sky-radiometer observations of precipitable water vapor

2019 ◽  
Author(s):  
Masahiro Momoi ◽  
Rei Kudo ◽  
Kazuma Aoki ◽  
Tatsuhiro Mori ◽  
Kazuhiko Miura ◽  
...  
Keyword(s):  
Optical Properties ◽  
Water Vapor ◽  
Solar Irradiance ◽  
Precipitable Water ◽  
Dry Season ◽  
Calibration Constant ◽  
Aerosol Optical Properties ◽  
Vapor Channel ◽  
Long Term Observation

Abstract. The Prede sky-radiometer, whose aerosol channels are calibrated by on-site measurements (the Improved Langley method), has been used for continuous long-term observation of aerosol properties. However, continuous long-term observation of precipitable water vapor (PWV) by sky-radiometer remain challenge, because the water vapor channel is generally calibrated by the standard Langley method at limited observation sites (e.g., the Mauna Loa Observatory). In this study, we developed SKYMAP, a new onsite self-calibration method for the water vapor channel of the Prede sky-radiometer using diffuse radiances normalized by direct solar irradiance. The SKYMAP algorithm consists of three steps. First, aerosol optical and microphysical properties are retrieved using direct solar irradiances and the normalized diffuse radiances at aerosol channels. The aerosol optical properties at the water vapor channel are interpolated from those at aerosol channels. Second, the transmittance of PWV is retrieved using the diffuse radiance normalized to the direct solar irradiance at the water vapor channel, which does not need the calibration constant. Third, the calibration constant at the water vapor channel is estimated from the transmittance of PWV and aerosol optical properties. Intensive sensitivity tests of SKYMAP using simulated data of the sky-radiometer showed that the calibration constant is retrieved reasonably well for PWV < 2 cm, indicating that SKYMAP can calibrate the water vapor channel on-site in dry conditions. Then SKYMAP was applied to actual measurements in the dry season at two sites (Tsukuba and Chiba, Japan). Because the SKYMAP algorithm is useful for clear-sky and low PWV (< 2 cm) conditions, the water vapor channel was calibrated for the dry season. After determining the calibration constant, PWV is able to be retrieved using direct solar irradiances for the whole year. The retrieved PWV values correspond well to those derived from a Global Navigation Satellite System (GNSS)/Global Positioning System (GPS) receiver, a microwave radiometer, and a AERONET sun-sky radiometer at both sites (correlation coefficient γ > 0.96), indicating that the Prede sky-radiometer provides both aerosol and PWV data based on its unique on-site calibration methods.

scholarly journals Development of on-site self-calibration and retrieval methods for sky-radiometer observations of precipitable water vapor

2020 ◽  
Vol 13 (5) ◽  
pp. 2635-2658 ◽  
Author(s):  
Masahiro Momoi ◽  
Rei Kudo ◽  
Kazuma Aoki ◽  
Tatsuhiro Mori ◽  
Kazuhiko Miura ◽  
...  
Keyword(s):  
Water Vapor ◽  
Root Mean Square ◽  
Solar Irradiance ◽  
Calibration Method ◽  
Bias Error ◽  
Mean Square ◽  
Calibration Constant ◽  
Vapor Channel ◽  
Self Calibration

Abstract. The Prede sky radiometer measures direct solar irradiance and the angular distribution of diffuse radiances at the ultraviolet, visible, and near-infrared wavelengths. These data are utilized for the remote sensing of aerosols, water vapor, ozone, and clouds, but the calibration constant, which is the sensor output current of the extraterrestrial solar irradiance at the mean distance between Earth and the Sun, is needed. The aerosol channels, which are the weak gas absorption wavelengths of 340, 380, 400, 500, 675, 870, and 1020 nm, can be calibrated by an on-site self-calibration method, the Improved Langley method. This on-site self-calibration method is useful for the continuous long-term observation of aerosol properties. However, the continuous long-term observation of precipitable water vapor (PWV) by the sky radiometer remains challenging because calibrating the water vapor absorption channel of 940 nm generally relies on the standard Langley (SL) method at limited observation sites (e.g., the Mauna Loa Observatory) and the transfer of the calibration constant by a side-by-side comparison with the reference sky radiometer calibrated by the SL method. In this study, we developed the SKYMAP algorithm, a new on-site method of self-calibrating the water vapor channel of the sky radiometer using diffuse radiances normalized by direct solar irradiance (normalized radiances). Because the sky radiometer measures direct solar irradiance and diffuse radiance using the same sensor, the normalization cancels the calibration constant included in the measurements. The SKYMAP algorithm consists of three steps. First, aerosol optical and microphysical properties are retrieved using direct solar irradiances and normalized radiances at aerosol channels. The aerosol optical properties at the water vapor channel are interpolated from those at aerosol channels. Second, PWV is retrieved using the angular distribution of the normalized radiances at the water vapor channel. Third, the calibration constant at the water vapor channel is estimated from the transmittance of PWV and aerosol optical properties. Intensive sensitivity tests of the SKYMAP algorithm using simulated data of the sky radiometer showed that the calibration constant is retrieved reasonably well for PWV<2 cm, which indicates that the SKYMAP algorithm can calibrate the water vapor channel on-site in dry conditions. Next, the SKYMAP algorithm was applied to actual measurements under the clear-sky and low-PWV (<2 cm) conditions at two sites, Tsukuba and Chiba, Japan, and the annual mean calibration constants at the two sites were determined. The SKYMAP-derived calibration constants were 10.1 % and 3.2 % lower, respectively, than those determined by a side-by-side comparison with the reference sky radiometer. After determining the calibration constant, we obtained PWV from the direct solar irradiances in both the dry and wet seasons. The retrieved PWV values corresponded well to those derived from a global-navigation-satellite-system–global-positioning-system receiver, a microwave radiometer, and an AERONET (Aerosol Robotic Network) sun–sky radiometer at both sites. The correlation coefficients were greater than 0.96. We calculated the bias errors and the root mean square errors by comparing PWV between the DSRAD (direct solar irradiance) algorithm and other instruments. The magnitude of the bias error and the root mean square error were <0.163 and <0.251 cm for PWV<3 cm, respectively. However, our method tended to underestimate PWV in the wet conditions, and the magnitude of the bias error and the root mean square error became large, <0.594 and <0.722 cm for PWV>3 cm, respectively. This problem was mainly due to the overestimation of the aerosol optical thickness before the retrieval of PWV. These results show that the SKYMAP algorithm enables us to observe PWV over the long term, based on its unique on-site self-calibration method.

Aerosol optical properties and precipitable water vapor column in the atmosphere of Norway

2015 ◽  
Vol 54 (6) ◽  
pp. 1505 ◽  
Author(s):  
Dennis Muyimbwa ◽  
Øyvind Frette ◽  
Jakob J. Stamnes ◽  
Taddeo Ssenyonga ◽  
Yi-Chun Chen ◽  
...  
Keyword(s):  
Optical Properties ◽  
Water Vapor ◽  
Precipitable Water ◽  
Precipitable Water Vapor ◽  
Aerosol Optical Properties

scholarly journals Aerosol optical properties and their effect on the UV solar irradiance at Uccle, Belgium

2013 ◽  
Author(s):  
Efterpi Nikitidou ◽  
Veerle De Bock ◽  
Hugo De Backer ◽  
Andreas Kazantzidis
Keyword(s):  
Optical Properties ◽  
Solar Irradiance ◽  
Aerosol Optical Properties

Representation of aerosol optical properties using a chemistry transport model to improve solar irradiance modelling

Solar Energy ◽  
2018 ◽  
Vol 176 ◽  
pp. 439-452 ◽  
Author(s):  
Karine Sartelet ◽  
Carole Legorgeu ◽  
Lya Lugon ◽  
Yassine Maanane ◽  
Luc Musson-Genon
Keyword(s):  
Optical Properties ◽  
Solar Irradiance ◽  
Transport Model ◽  
Aerosol Optical Properties ◽  
Chemistry Transport Model

scholarly journals Column ozone and aerosol optical properties retrieved from direct solar irradiance measurements during SOLVE II

2004 ◽  
Vol 4 (6) ◽  
pp. 7403-7431
Author(s):  
W. H. Swartz ◽  
J.-H. Yee ◽  
R. E. Shetter ◽  
S. R. Hall ◽  
B. L. Lefer ◽  
...  
Keyword(s):  
Optical Properties ◽  
Solar Irradiance ◽  
Aerosol Optical Properties ◽  
Ozone Loss ◽  
Spectral Fitting ◽  
Validation Experiment ◽  
Measurement Validation ◽  
Column Ozone ◽  
Spectral Solar Irradiance ◽  
Good Agreement

Abstract. Direct observation of the Sun at large solar zenith angles during the second SAGE III Ozone Loss and Validation Experiment (SOLVE II)/Validation of International Satellites and study of Ozone Loss (VINTERSOL) campaign by several instruments provided a rich dataset for the retrieval and analysis of line-of-sight column composition, intercomparison, and measurement validation. A flexible, multi-species spectral fitting technique is presented and applied to spectral solar irradiance measurements made by the NCAR Direct beam Irradiance Atmospheric Spectrometer (DIAS) on-board the NASA DC-8. The approach allows for the independent retrieval of O3, O2·O2, and aerosol optical properties, by constraining Rayleigh extinction. We examine the 19 January 2003 and 6 February 2003 flights and find very good agreement of O3 and O2·O2 retrievals with forward-modeling calculations, even at large solar zenith angles, where refraction is important. Intercomparisons of retrieved ozone and aerosol optical thickness with results from the Ames Airborne Tracking Sunphotometer (AATS-14) are summarized.

Statistical Characteristics of Long-Term High-Resolution Precipitable Water Vapor Data at Darwin

2018 ◽  
Vol 10 (04) ◽  
pp. 1850010
Author(s):  
Kimberly Leung ◽  
Aneesh C. Subramanian ◽  
Samuel S. P. Shen
Keyword(s):  
Water Vapor ◽  
High Resolution ◽  
Southern Oscillation ◽  
Precipitable Water ◽  
Precipitable Water Vapor ◽  
Statistical Characteristics ◽  
Convective Precipitation ◽  
Data Set ◽  
Best Estimates

This paper studies the statistical characteristics of a unique long-term high-resolution precipitable water vapor (PWV) data set at Darwin, Australia, from 12 March 2002 to 28 February 2011. To understand the convective precipitation processes for climate model development, the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) program made high-frequency radar observations of PWV at the Darwin ARM site and released the best estimates from the radar data retrievals for this time period. Based on the best estimates, we produced a PWV data set on a uniform 20-s time grid. The gridded data were sufficient to show the fractal behavior of precipitable water with Hausdorff dimension equal to 1.9. Fourier power spectral analysis revealed modulation instability due to two sideband frequencies near the diurnal cycle, which manifests as nonlinearity of an atmospheric system. The statistics of PWV extreme values and daily rainfall data show that Darwin’s PWV has El Nino Southern Oscillation (ENSO) signatures and has potential to be a predictor for weather forecasting. The right skewness of the PWV data was identified, which implies an important property of tropical atmosphere: ample capacity to hold water vapor. The statistical characteristics of this long-term high-resolution PWV data will facilitate the development and validation of climate models, particularly stochastic models.

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