Abstract
Abstract. Extraterrestrial spectral response calibration of a multi-filter rotating shadow band radiometer (MFRSR) under pristine Amazonian Forest atmosphere conditions was performed using the Langley plot method. The MFRSR is installed in central Amazonia as part of a long-term monitoring site, which was used in the context of the GoAmazon2014/5 experiment. It has been operating continuously since 2011 without regular extraterrestrial calibration, preventing its application to accurate monitoring of aerosol particles. Once calibrated, the MFRSR measurements were applied to retrieve aerosol particle columnar optical properties, specifically aerosol optical depth (AODλ) and Ångström exponent (AE), which were evaluated against retrievals from a collocated Cimel Sun photometer belonging to the AErosol RObotic NETwork (AERONET). Results obtained revealed that pristine Amazonian conditions are able to provide MFRSR extraterrestrial spectral response with relative uncertainty lower than 1.0 % in visible channels. The worst estimate (air mass =1) for absolute uncertainty in AODλ retrieval varied from ≈0.02 to ≈0.03, depending on the assumption regarding uncertainty for MFRSR direct normal irradiance measured at the surface. The obtained root mean square error (RMSE ≈0.025) from the evaluation of MFRSR retrievals against AERONET AODλ was, in general, lower than estimated MFRSR AODλ uncertainty, and close to the uncertainty of AERONET field Sun photometers (≈0.02).
Highlights
Aerosol optical depth (AOD) is an important variable for characterizing atmospheric particles’ columnar abundance and is fundamental in estimating their direct radiative forcing in the climate system (Shaw, 1983; Kaufman et al, 2002; Menon, 2004; Satheesh and Srinivasan, 2005)
The question that drives the focus of the present study is as follows: do pristine central Amazonian atmosphere conditions provide successful scenarios for extraterrestrial response calibration? The Amazonian atmosphere under pristine conditions has been denominated as green ocean due to its very low pollution concentration, comparable to remote ocean areas (Roberts et al, 2001; Andreae et al, 2004), which is a fundamental requirement for applying the Langley plot method
Does the pristine central Amazonian atmosphere provide successful extraterrestrial response calibration based on the Langley plot method? This question emerged from the challenge of maintaining regular calibration of a multi-filter rotating shadow band radiometer (MFRSR) dedicated to long-term retrieval of columnar aerosol optical properties in the central Amazon
Summary
Aerosol optical depth (AOD) is an important variable for characterizing atmospheric particles’ columnar abundance and is fundamental in estimating their direct radiative forcing in the climate system (Shaw, 1983; Kaufman et al, 2002; Menon, 2004; Satheesh and Srinivasan, 2005). Given the inherent complex logistics that characterize field experiments in Amazonia, regular trips to distant, clean mountaintops to perform ERC of AOD monitoring devices operating inside the forest are a challenge, mainly for long-term sites. An experimental site, located in central Amazonia, and included in the context of the Observations and Modelling of the Green Ocean Amazon (GoAmazon2014/5, Martin et al, 2016), under the reference T0e, is operating since 2011 a MFRSR as part of a set of instruments for performing long-term atmospheric monitoring of convection, radiation, aerosols, and cloud properties in central Amazonia (Barbosa et al, 2014). The MFRSR is being operated at the T0e site since 2011 without performing its ERC, which prevent its application to retrieve AOD In this context, the question that drives the focus of the present study is as follows: do pristine central Amazonian atmosphere conditions provide successful scenarios for extraterrestrial response calibration?
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