Abstract
Feasibility of precipitable water vapor (PWV) retrieval from the ground-based infrared measurements in clear sky conditions was performed based on the radiative transfer simulation and retrieval experiments. The effects of aerosol, view zenith angle, and instrument spectral response function (SRF) on clear-sky infrared brightness temperature ( T sky) were analyzed. The results showed that atmospheric aerosol and SRF have obvious influence on T sky measurements and PWV retrievals. The relationship between T sky and PWV under low aerosol loading conditions is better than that of high aerosol loading conditions. Aerosol information is necessary for the inversion of high-precision PWV using a single-angle T sky measurement. T sky at the infrared atmospheric window (i.e., 10 to 12 μm) has a better exponential relationship with PWV than that covers 6.3 μm water vapor and 9.6 μm ozone absorption bands. Furthermore, a neural network (NN)-based PWV retrieval algorithm was proposed using dual-angle T sky measurements and near-surface air temperature ( T air). The results showed that the introduction of multiangle T sky can effectively reduce the influence of aerosol on PWV retrieval and improve the PWV retrieval accuracy. The determination coefficient, root-mean-square error, and bias of the NN model using dual-angle T sky (i.e., 0 deg and 30 deg) and T air were 0.989, 0.191, and 0.002 cm, respectively.
Highlights
Water vapor in the atmosphere and its changes are the main drivers of weather and climate change.[1,2] It has important applications in precipitation and severe weather forecasting, atmospheric radiation research, water cycle, and global climate change research.[2,3] Precipitable water vapor (PWV) is the total atmospheric water vapor contained in a vertical column of unit cross-sectional area extending from the Earth’s surface to the top of the atmosphere
The Tsky of mid-latitude summer (MLS) atmosphere over 10 to 12 μm is below 240 K, whereas that of mid-latitude winter (MLW) atmosphere can be lower than 170 K
The results showed that the spectral response function (SRF), view zenith angle (VZA), and aerosol loading have significant effects on Tsky and PWV retrievals
Summary
Water vapor in the atmosphere and its changes are the main drivers of weather and climate change.[1,2] It has important applications in precipitation and severe weather forecasting, atmospheric radiation research, water cycle, and global climate change research.[2,3] Precipitable water vapor (PWV) is the total atmospheric water vapor contained in a vertical column of unit cross-sectional area extending from the Earth’s surface to the top of the atmosphere. A number of techniques have been used to obtain the PWV such as radiosonde, GPS, microwave radiometer, ground-based sun photometer, and satellite remote sensing.[8,9,10] Radiosonde can provide high precision water vapor products, but it is usually released twice per day and its typical spatial resolution is about 200 to 300 km.[11,12] Satellite remote sensing can provide. Ground-based remote sensing techniques such as microwave radiometer, GPS, sun photometer, and laser radar can measure PWV with high accuracy and high temporal resolution.[1,9,15,16,17] the ground-based remote sensing equipment is generally expensive and not convenient to carry. The feasibility of PWV retrieval for several SRFs under different atmospheric aerosol models were analyzed based on the radiative transfer simulations and retrieval experiments
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