The Shale Hills watershed has a comprehensive base of instrumentation for physical, chemical and biological characterization of water, energy, stable isotopes and geochemical conditions. This includes a dense network of soil moisture observations at multiple depths (120), a shallow observation well network (24 wells), soil lysimeters at multiple depths (+80), a COSMOS soil moisture instrument, a research weather station including eddy flux measurements for latent and sensible heat flux, CO2, and water vapor, radiation, barometric pressure, temperature, relative humidity, wind speed/direction, snow depth sensors, leaf wetness sensors, a load cell precipitation gauge. A laser precipitation monitor (LPM: rain, sleet, hail, snow, etc.) was installed in 2008, as were automated water samplers (daily) for precipitation, groundwater, and stream water for chemistry and stable isotopes with weekly sampling of lysimeters. Arrays of sapflow measurements are carried out each year as a function of tree species (25 species in the watershed). Geochemical measurements for solution chemistry, isotopes, electrical conductance and potential are carried out weekly on the soil lysimeter profiles, stream, groundwater and precipitation. The field-deployed sensor network is connected on a combined mesh and LAN wireless system.
A 15 amp, 120 volt service was completed in July 2008, including lightning and surge protection. Power was tied off at a newly constructed small communications building located at the entrance to the watershed. Extensions of that tie-off have been run to the eddy flux and wireless communication tower, the stream gauge at the Shale Hills outlet, and the sap flow experiment. Other outlets have been requested and were installed in 2009-10 and continue to be installed as needed. A 30m tower was installed in 2008 to provide a meso-scale link from the watershed to the university and to provide the backbone for real-time observations. A 5.7 GHz Motorola multipoint access wireless system was installed by a local IP to serves Shale Hills and the larger Stone Valley Experimental Forest with internet communications. The tower, located 300m from the power lines and communication building, is also our main meteorological research site. Ethernet and power were installed in 2008-09. In Dec. 2010 the Ethernet was replaced with a 3-mode fiber optic cable. The system also supports the Shaver’s Creek Environmental Center for which they have their own access point where they will create a virtual classroom for K-12 education onsite at the center.
From 2005-2009 the main observing network was based on Campbell Scientific data loggers that are maintained manually except for the RTH_NET sites which use a Free Wave 900 MHz radio. The 900MHz antennas and radios connects the RTH_NET arrays to the wireless communications system backbone. These sites include a below-canopy met station, groundwater levels, soil moisture profiles and stream stage observations. A soil moisture network of some 120 sites is maintained manually by Henry Lin’s group based on CSI data loggers. Dave Eissenstat’s group maintains a sapflow network that also uses CSI loggers which are maintained manually. A 3rd CSI manual network has recently been implemented for redox and dissolved oxygen measurements. The wireless network at the meteorological station is backed up using the fiber optic cable to a server in the communications shed.
Campbell Scientific data loggers operating within the catchment, i.e. those with poor line-of-sight to the wireless nodes on RTH_NET, form a mesh network. Wireless ad-hoc networks are packet based, multi-hop, radio networks consisting of mobile wireless nodes communicating over a shared wireless channel. The Figure below illustrates the design for the current mesh network structure. This architecture allows wireless access to data loggers that were previously serviced manually.
Detailed diagram of the wireless network at SSHCZO. The mesh network will provide flexibility of communication in the lower part of the catchment where line-of-sight between communication nodes is poor. At the ridge top (RTH1) and stream outlet (Communications Shed) direct connections are made to servers on the PSU campus.
1) Scalability: An environmental ad hoc network can theoretically grow to hundreds of nodes. For wireless network infrastructures, scalability is achieved by a hierarchical construction. However, in the forest canopy we have found that ~ 1 node per acre is optimal for communication.
2) Multi-hopping: A multi-hopping network is one in which the path from a source to a destination traverses several other nodes. Environmental changes as well as changes in the density of foliage render a highly variable radio propagation path. Thus, whenever a direct path is unavailable from a source to a destination, ad-hoc networks have the capability to route the data via other nodes increasing reliability.
3) Self-organization: The ad hoc network autonomously determines its own configuration parameters including addressing, routing, power control.
4) Web Access to Field Data: The mesh and wireless networks allow users on campus to view data directly from specific data loggers. Automatic warning messages are triggered for sensor failure or erroneous readings.
5) Security: OpenWRT protocols control network access via a VPN. This prevents malicious entry into the sensor network and ensures good data quality.
Leaf Area Index (LAI), greenness index , microbial composition, distribution and CO2 flux are regularly carried out. A complete suite of borehole logging was done at 3 locations to 17m. These include: (1) spectral gamma; (2) caliper- borehole diameter log to locate broken and fractured zone; (3) fluid resistivity- total dissolved solids in the water column (4) fluid temperature; (5) heat-pulse flowmeter- rate and direction of vertical flow in a borehole; and (6) optical tele-viewer for continuous, oriented, true-color 360° image of the borehole wall. Additionally hydraulic and tracer tests were done to estimate the effective hydraulic properties in all wells in the field.