H51N-01 INVITED
Some Recent Advances in Hydrologic and Atmospheric Sensor Technology
The long standing challenge that faces all hydrologists and atmospheric scientists is the spatial and temporal complexity of the land surface and the desire to have high resolution measurements of surface fluxes and various state variables. Three recent advances in sensor technology are discussed and their application in the field for improved understanding of hydrologic phenomena is presented: 1. A new generation high resolution scanning raman lidar to measure temperature and humidity simultaneously at 1 m resolution to a 500 m range along with field observations; 2. A multihop wireless sensor system (sensorscope) for hydrologic applications including over rugged alpine terrain; 3. Applications of raman optical fiber sensing of temperature along stream beds is discussed. The combination of these sensors to probe the environment is allowing smaller research teams to make rapid advances in understanding the water cycle across the landscape in regions previously not monitored at high resolution. http://eflum.epfl.ch
H51N-02
Microwave Links as Tools in Precipitation Measurement
Over the last decade there has been a growing awareness across Europe of the possibilities of using microwave links for the measurement of path-averaged precipitation. In the UK our research initially focused on the use of specially chosen dual-frequency links --- we will present a summary of that work, and of the possibilities that it presented for distinguishing between rain and melting snow. We will also reference recent work elsewhere in Europe that has examined the potential use of commercial links. However, our primary focus will be a presentation of the results of two current research endeavours. We will show that microwave links can perform a useful role as a successful substitute for rain gauges in the final stage of adjusting the estimates of rainfall from a weather radar. We will illustrate this with data from an operational UK Met Office radar. Our second current research area has been an investigation of the feasability of determining information about the drop-size distribution from examination of the differential phase of a link, with information transmitted at 45 degrees and with the horizontal and vertical components being separately received.
H51N-03
SoilNet - A Zigbee based soil moisture sensor network
Soil moisture plays a key role in partitioning water and energy fluxes, in providing moisture to the atmosphere for precipitation, and controlling the pattern of groundwater recharge. Large-scale soil moisture variability is driven by variation of precipitation and radiation in space and time. At local scales, land cover, soil conditions, and topography act to redistribute soil moisture. Despite the importance of soil moisture, it is not yet measured in an operational way, e.g. for a better prediction of hydrological and surface energy fluxes (e.g. runoff, latent heat) at larger scales and in the framework of the development of early warning systems (e.g. flood forecasting) and the management of irrigation systems. The SoilNet project aims to develop a sensor network for the near real-time monitoring of soil moisture changes at high spatial and temporal resolution on the basis of the new low-cost ZigBee radio network that operates on top of the IEEE 802.15.4 standard. The sensor network consists of soil moisture sensors attached to end devices by cables, router devices and a coordinator device. The end devices are buried in the soil and linked wirelessly with nearby aboveground router devices. This ZigBee wireless sensor network design considers channel errors, delays, packet losses, and power and topology constraints. In order to conserve battery power, a reactive routing protocol is used that determines a new route only when it is required. The sensor network is also able to react to external influences, e.g. such as rainfall occurrences. The SoilNet communicator, routing and end devices have been developed by the Forschungszentrum Juelich and will be marketed through external companies. We will present first results of experiments to verify network stability and the accuracy of the soil moisture sensors. Simultaneously, we have developed a data management and visualisation system. We tested the wireless network on a 100 by 100 meter forest plot equipped with 25 end devices each consisting of 6 vertically arranged soil moisture sensors. The next step will be the instrumentation of two small catchments (~30 ha) with a 30 m spacing of the end devices. http://www.fz- juelich.de/icg/icg-4/index.php?index=739
H51N-04 INVITED
Realtime Delivery of Alarms and Key Observables in a Deployed Hydrological Sensor Network
It has widely [1-3] been proposed that sensor networks are a good solution for environmental monitoring. However, this application presents a number of major challenges for current technology. In particular environmental science involves the study of coupled non-equilibrium dynamic processes that generate time series with non-stationary means and strongly dependent variables and which operate in the presence of large amounts of noise/interference (thermal, chemical and biological) and multiple quasi-periodic forcing factors (diurnal cycles, tides, etc). This typically means that any analysis must be based on large data samples obtained at multiple scales of space and time. In addition the areas of interest are large, relatively inaccessible and typically extremely hostile to electronic instrumentation. Our analysis of these factors has encouraged us to focus on this list of generic requirements; a) Node lifetime (between visits) should be 1 yr or greater b) Communication range should be ~250m c) Nodes should be portable, unobtrusive, low cost, etc. d) Networks are expected to be sparse since areas of interest are large and budgets are small However, the characteristics of each environment, the dominant processes operating in it and the measurements that are of interest are sufficiently different that the design of an appropriate sensor network solution is normally most determined by site specific constraints. Most importantly the opportunities for exploiting contextual correlation to disambiguate observations and improve the maintenance and robustness of a deployed sensor network are always site specific. We will describe the design and initial deployment of a hydrological sensor network we are developing to assess the hydro-dynamics of surface water drainage into Great Crowden Brook in the Peak District (UK). The complete network will observe soil moisture, temperature and rainfall on a number of transects across the valley, and will also investigate water quality parameters (colouration, turbidity, Ph) in the stream. GSM access for remote real time reporting of network status is only available from the hilltops so a multihop communication strategy is being used for communication from the valley floor. To minimise radio usage and maximise battery life we are reporting only those alarms and events that are judged to be of high priority by embedding a simple rule based decision engine in each node. The rule conditions are derived from spatio-temporal cross-correlation of the available sensor inputs. . We report on our initial experiments with correlating readings for management purposes, and offer some initial hypotheses regarding aspects of this that might be generic based on a comparison with data obtained in an earlier experiment in a marine setting [4]. 1. http://cens.ucla.edu/ 2. http://eyes.eu.org/ 3. http://www.ee.unimelb.edu.au/ISSNIP/ 4. J. Tateson, C. Roadknight, A. Gonzalez, T. Khan, S. Fitz, I. Henning, N. Boyd, C. Vincent, and I. W. Marshall. Real World Issues in Deploying a Wireless Sensor Network. In Workshop on Real-World Wireless Sensor Networks REALWSN'05, Stockholm, Sweden, June 2005
H51N-05
Weighing trees: Measuring interception and evaporation dynamics by monitoring sub- micrometer tree trunk compaction
Interception of rain and snow by tree crowns can be a significant part of the water balance. Rain, intercepted by leaves, that evaporates directly back into the atmosphere may make up 10% to 60% of total precipitation. In most forests, 2 mm or more is intercepted per rainfall event. Measuring interception and its subsequent evaporation is difficult. Measuring rain above and below the canopy is prone to noise. Radiometric measurements are difficult to calibrate. Here, we make use of the fact that water or snow intercepted by the crown compacts the trunk, simply following Hooke's law. By measuring the compaction, the amount of water stored in the crown can be measured. In practice, many problems have to be overcome before a good weight signal is obtained. For starters, 1 kg of water stored in a small tree causes a compaction of only 100 nm over a stretch of 1 m. Such small displacements can actually be measured relatively easily with special potentiometers. We used such displacement sensors together with quartz rods of 1m length, that were bolted to the trunk. Quartz was chosen to reduce the effect of temperature changes. In addition, the trees were insulated and kept at a constant temperature with heating wire. The main source of noise is bending by wind. By radially installing three sensors, wind effects could accounted for as well. Final measurement accuracies of 1 kg to 5g were obtained, depending on tree size. Tree weighing results from Europe and Africa will be presented. http://www.smallreservoirs.org/trees.htm
H51N-06
Automated Lagrangian Water-Quality Assessment System (ALWAS) Measurements of North Slope Lakes and the Bering Glacier, Alaska
ALWAS is an inexpensive, free-floating, sail-powered or jet-driven water quality measuring and watershed evaluation buoy. It is capable of measuring data points with multiple parameters (depth, temperature, conductivity, salinity, total dissolved solids, dissolved oxygen, pH, oxidation reduction potential, turbidity, chlorophyll-a, blue-green algae, nitrate, ammonium, chloride, latitude/longitude, date, time, speed, and barometric pressure) as rapidly as every 40 seconds. Data is transmitted for real-time viewing and is stored for future retrieval and analysis. The collected data are easily downloaded into geographic databases (ESRI shapefile) and spreadsheet formats. ALWAS uses state-of-the-art sensors to measure water quality parameters and GPS data. Field demonstrations of the ALWAS technology from the Bering Glacier and the North Slope of Alaska will be presented. The ALWAS buoy will also be described as well as ALWAS data sharing, web-based mapping, and decision support tools.
H51N-07 INVITED
High Resolution Water Quality Monitoring: New Equipment, New Data, New Insights
Monitoring nutrient transfers in river catchments is often constrained by the need to analyse water samples in the laboratory. This can result in coarse sampling regimes that bias datasets to low flow or high flow periods depending on the sophistication of the sampling method. Subsequent statistical interpolation and extrapolation methods to estimate annual nutrient transfers rely on concentration-flow relationships that are often unpredictable and usually under-estimate observed loads. Coupled with this limitation is an inability to discern subtle patterns that may be un-sampled or overlooked as analytical ‘noise'. Here we present results from a novel and robust catchment monitoring method in an investigation of the magnitude, processes and patterns of total phosphorus (TP) transfers measured at high resolution. Bank-side TP analysers in the Irish border region extract and analyse TP in water samples on a 10 min time-step in 3x5km2 sub-catchments of the Blackwater River. Other, complimentary, water quality and hydrometeorological parameters are also measured continuously using standard and established equipment. The datasets provide a time-integrated series that can establish observed annual TP loads for catchment management. Additionally, storm related transfers from diffuse sources are fully captured and indicate periods of nutrient ‘wash-out' and relationships with frontal and convective precipitation. Low flow TP transfers indicate impacts from rural point-sources and also diurnal changes due to processes that are only partially understood. The datasets can also be used to validate interpolation methods from coarser sampling regimes and provide unsurpassed time-series validation for catchment water quality models.