As a result of an MoU which was signed by the NUST vice chancellor, Prof Tjama Tjivikua and NASA late in 2015, the development of a NASA-AERONET network around Namibia has been facilitated. From 9-15 February 2016, with the support of a NASA-AERONET visiting engineer, Mikhail Sorokin, the department of Geo-Spatial Sciences and Technology (GST) at NUST worked on the installation of an AERONET robotic network around Namibia. Five CIMEL sunphotometers were installed at various locations. Two photometers maintained by North West University are already in place at the Gobabeb Research and Training Centre and the UNAM campus at Henties Bay, bringing to seven the total number of photometers in the Namibian AERONET network. One of the five instruments which has been installed at NUST, is temporary, and will later this year be relocated to Possession Island. The location of the photometer network can be seen in the figure alongside. The installation of this network would not be possible without the support of individual farmers and institutes that have shown a willingness to have these instruments installed on their properties.
A sun photometer collects Aerosol Optical Depth (AOD) readings at 15 minute intervals, in 8 different wavelengths, throughout daylight hours. Newer models are now able to do lunar collections between the ¼ -- ¾ moon cycle. The AOD measurements give us an idea on the quantity of aerosols in the atmosphere. The data from the CIMEL photometer is uploaded directly to the NASA AERONET division, and after being briefly checked for data quality issues it is made freely accessible and available online (http://aeronet.gsfc.nasa.gov/new_web/index.html). An example of variability of the AOD observed at these different sites is shown in the figure below which shows the AOD at 1640nm at 6 of the different Namibian sites from the 1-22 March 2016 (Julian Day 61-82). Note that the data displayed in this graph is level 1 data which has not been cloud screened. The very high figures will probably disappear after the cloud contamination has been removed in the level 1.5 and 2 data. Links to the site data and photo’s of the five AERONET stations which have been installed under the NUST/NASA MoU are provided at the end of this article.
Although Namibia in general has clear atmospheric conditions it does experience a variety of different aerosols at different times of the year in different locations, for example fog, and marine aerosols off our coastline, dust from the Etosha Pan, and burning biomass, some of which originates from within Namibia, but most of it which is transported over Namibia from the neighbouring countries (creating the haze that we see particularly in Aug-Sept months). One of the long term plans that we in the GST department of NUST have for using this AERONET data is to develop models which are temporally and spatially adaptive for atmospheric correction of satellite images acquired in our region. This component of research is a small contribution to a larger research initiative which will focus on aerosols and how they link between the Sea-Earth & Atmosphere (primarily along the west coast of southern Africa). This is a long term project envisioned to stretch over about a 10-15 year timeframe, and is being driven as a national, regional and international scientific initiative under a research banner called the Sea-Earth-Atmosphere Linkages Study in southern Africa (SEALS-sA).