CosmOz Newsletter, April 2013
Welcome to the April 2013 CosmOz newsletter. This month we introduce the South-east Esk Hydrological Sensor Web study and discuss the simple correction that is required to adjust cosmic ray neutron data for changes in atmospheric humidity. We will also update you on the latest publications in the field and the upcoming CosmOz workshop.
South Esk Project
One of the first Australian projects to utilise a cosmic-ray neutron soil moisture probe is the South Esk Hydrological Sensor Web. The South Esk Hydrological Sensor Web is an open web-based data infrastructure that federates near real-time hydro-meteorological data collected by several organisations in the South Esk River catchment in NE Tasmania. The project started in July 2008 with the aim of better informing water managers about resource availability and water harvesting opportunities while also protecting environmental flows.
Figure 1. (Left) Location of the South Esk Hydrological Sensor web project showing hydrological data collection points. (Right) The cosmic-ray probe which has been incorporated into the sensor web.
Data collected across the sensor web are harmonised and used as inputs to a hydrological model that predicts river flows on a continuous basis. An open architecture is used to allow data sources and predictive models to be easily substituted. Such adaptability means the data infrastructure can be easily re-purposed for different applications e.g. bushfire spread modelling and/or irrigation decision support.
The South Esk Hydrological Sensor Web includes a cosmic-ray soil moisture probe deployed at Tullochgorum which will be used to check whether soil moisture estimates from the continuous flow forecast model are realistic or not. This information will be used to calculate uncertainty in flow forecasts. The existing probe has been operational since December 2010 and there are plans to install two additional probes in the near future.
Cosmic-ray atmospheric humidity corrections
Last issue we talked about the need to apply simple corrections to cosmic ray neutron count data to account for background levels of incoming cosmic-rays, this issue we will discuss the simple corrections which are required to account for changes in atmospheric humidity. Water in the atmosphere in the form of vapour represents a further source of hydrogen in the cosmic-ray probe ‘footprint’ which can influence the cosmic-ray neutron counts. Seeing as we are primarily interested in soil moisture information this may be seen as a problem, however, a simple correction has been developed (Rosolem et al. 2012) which enables us to modify neutron counts depending on whether the atmosphere is wetter or drier than on a selected arbitrary reference date. An example of the correction multiplier applied is shown in Figure 2 for Weany Creek in the dry tropics. In this example a reference date in May is selected and counts from more humid periods (wet season) are increased (multiplier >1) to account for neutron counts lost to additional atmospheric hydrogen. Conversely, counts in the drier atmospheric conditions during the dry season are reduced (multiplier <1) to account for a smaller impact of atmospheric hydrogen on the measured signal. The correction is simple to apply and only requires supplementary measurements of temperature and humidity. Across a year the humidity correction affect counts by around ±4%.
Figure 2. Corrections applied to cosmic-ray probe data at Weany Creek to account for changes in atmospheric humidity when moving between wet and dry seasons. Corrections are made relative to the humidity on the reference date in May.
Rosolem R, Shuttleworth J, Zreda M, Zweck C, Franz T and Zeng X (2012) The Effect of Atmospheric Water Vapor on the Cosmic-ray Soil Moisture Signal. EGU General Assembly 2012. Geophysical research Abstracts, Vienna.
The CosmOz workshop in Brisbane will be held on the 22nd and 23rd of May at the EcoSciences Precinct. The aim is to get interested parties and probe managers together to talk about where we have got to with the CosmOz network over the last couple of years. Topics to be discussed include interesting data sets and analysis, calibration progress, linkages to other projects, data delivery, future research direction and funding opportunities. If you have an interest in attending and have not yet let us know please contact Dave McJannet.
New papers recently published:
· Desilets D and Zreda M (2013) Footprint diameter for a cosmic-ray soil moisture probe: Theory and monte carlo simulations. Water Resources Research, DOI: 10.1002/wrcr.20187
· Rivera Villarreyes CA, Baroni G and Oswald SE (2013) Calibration approaches of cosmic-ray neutron sensing for soil moisture measurement in cropped fields. Hydrol. Earth Syst. Sci. Discuss. 10(4), 4237-4274. DOI: 10.5194/hessd-10-4237-2013
The CosmOz network is actively engaged with the OzEWEX Observational Data Working Group which aims to promote awareness, access and continuity of existing observation data sources that are critical for research of the energy and water cycle, and to evaluate new observations.