Retrieval of calibration parameters for ground based Sun-Sky radiometric measurements of columnar water vapor using operational surface meteorological measurements

[ABSTRACT]Sun-sky radiometers are instruments created for aerosol study, but they can measure in the water vapour absorption band allowing the estimation of columnar water vapour W in clear sky simultaneously with aerosol characteristics, with high temporal resolution. A new methodology, cheap and easy to implement, is presented for estimating calibration parameters (i.e. characteristic parameters of the atmospheric transmittance and solar calibration constant) directly from the sun-sky radiometers measurements. To initiate the proposed methodology some seasonal independent measurements of columnar water vapour taken over a large range of solar zenith angle simultaneously with the sun-sky radiometer measurements, are needed. In this work the Surface Humidity Method (SHM) was developed allowing to initiate the procedure with columnar water vapour estimated by standard surface meteorological observation (temperature, pressure and relative humidity). The time pattern of columnar water vapour from sun-sky radiometer was compared with simultaneous measurements from microwave radiometer and radiosondings showing respectively a total correlation of 0.98, 0.96 and a total median difference of 2.24 mm and -0.65 mm. The accordance with radiosondings was found within the uncertainty of the methodology (varying from 10 to 16 %) independently on the amount of atmospheric water vapour. Results were also validated against the columnar water vapour estimated by using the procedure adopted by the University of Uchiyama, that is similar to the one adopted by AERONET network, and consists in retrieving the characteristic parameters from a fitting procedure of simulated transmittance versus the product mW, were m is the optical airmass. Also in this case the accordance against microwave radiometer and radiosondings is good for different water vapour classes, but we like to emphasize that the introduction of a water vapour dependence in the characteristic parameters of the atmospheric transmittance, improved the agreement with the Microwave Radiometer measurements especially in the cases with the lowest water vapour content.

https://opac.ll.chiba-u.jp/da/curator/107444/

https://opac.ll.chiba-u.jp/da/curator/107444/ceresIntlSympo-19-P013.pdf

Chiba University. Center for Environmental Remote Sensing

千葉大学環境リモートセンシング研究センター

会議発表用資料

Proceedings of the CEReS international symposium = CEReS国際シンポジウム資料集

19

13

14

2013-07-04

publisher

環境リモートセンシング研究センター「CEReSシンポジウム資料集」