Automatic low-cost radiometer for dust monitoring in desert areas
There are extensive networks of ground sun-photometers for aerosol monitoring all over the world. They are integrated by very precise instruments, with an accuracy close to 0.02 in the retrievals of aerosol optical depth (AOD) in the visible spectral range (this value is the goal set by World Meteorological Organization). However, there is a lack of stations in desert regions of the Northern Hemisphere, which are the most important sources of mineral dust, mainly due to the high cost of these sophisticated instruments, the need of trained staff to operate them and the high power consumption. The consequence of this lack of information is the unsatisfactory description of dust cycles.
A recent study presents a new zenith-looking narrow-band radiometer-based system (ZEN), conceived for dust AOD monitoring. The ZEN consists of a ZEN-R41 radiometer, which measures downwelling zenith sky radiance (ZSR) at four channels (870, 675, 500 y 440 nm) and a methodology for AOD retrieval (ZEN-LUT). The ZEN-R41 radiometer, (Figure) designed to be stand-alone and without moving parts, is a low-cost, robust and automated instrument with lower maintenance than ordinary sun-photometers. Thus, it is suitable to be deployed in remote and unpopulated desert areas. The ZEN-LUT method, based on methodologies applied to satellite sensors, uses a radiative transfer code to simulate the ZSRs and their associated AODs. This method has been developed using information from Cimel-AERONET sun-photometers.
The results of the preliminary study, conducted at Izaña and Santa Cruz de Tenerife (Canary Islands, Spain) and Tamanrasset (Algeria) suggests that the ZEN-LUT method is appropriate to infer dust AOD from ZSR ZEN-R41 measurements. The comparison between ZEN-LUT and AERONET retrievals yields correlations (R2) ranging from 0.99 for Santa Cruz and 0.97 for Tamanrasset. The conclusion is that ZEN is a suitable system to fill the current observational gaps and to complement observations performed by current sun-photometer networks in order to improve mineral dust monitoring in remote locations. As a consequence, it can play a key role to provide information for data assimilation into numerical models, validation of satellite products and early warning systems within the WMO Sand and Dust Storm - Warning Advisory and Assessment System (SDS WAS).
Development of instrument and retrieval methodology has been entirely conceived, designed, implemented and validated at the Izaña Atmospheric Research Center, as one of the activities of Izaña WMO-CIMO Testbed for Aerosols and Water Vapor Remote Sensing Instruments.
Further details on this study can be found at:
Almansa, A. F., Cuevas, E., Torres, B., Barreto, Á., García, R. D., Cachorro, V. E., de Frutos, Á. M., López, C., and Ramos, R.: A new zenith-looking narrow-band radiometer-based system (ZEN) for dust aerosol optical depth monitoring, Atmos. Meas. Tech., 10, 565-579, doi:10.5194/amt-10-565-2017, 2017.