2 Field installation
A hybrid displacement monitoring system was developed. It consists of two different types of GPS-receivers and the groundbased InSAR device IBIS-L. The system design as installed at Lagoa de Fogo, Sao Miguel, Acores is described below. The stations were meant to work independent and self-sustaining in the months April to September, for other regions, environmental circumstances and/or different hardware (i.e. with different consumption of electricity) the power supply dimensioning has to be adjusted.
- Fig. 2.1 Configuration of a GPS-Station
- Fig. 2.2 Low-cost GPS-Station at Lagoa de Fogo, Sao Miguel, Azores
2.1 Installation of GPS-Stations
There were two kind of GPS-stations installed: the low-cost single-frequency-receiver stations and the precise double-frequency-receiver stations.
The low cost stations were located directly in the high risk area, monitored by the IBIS-L instrument. They included therefore ground reflectors, to echo the radar signal. The precise geodetic double frequency stations were located farther away from the monitored area.
Figure 2.1 gives the basic configuration of a GPS-station. Each station had two masts of at least 2m height. One for the GPS-antenna and one for the WLAN-antenna and the solar panels. The instruments were stored in a wooden box, fixed to one of the masts. Below a detailed list of equipment is given.
Equipment of a typical single frequency receiver station
GPS-Receiver ublox Antaris 4
GPS-Antenna Plate
Meshnode
PoE
electr. Accessories (Cable, plugs…)
Meshnode WLAN Antennas
Environment Sensors
Battery (60Ah)
Solarpanel 50 Wp
Mountings for Solarpanel
Mountings for Reflectors
Reflector
Steel Pipe (3m)
Steel Pipe (2m)
Steel Pipe (1m)
Device Box
Equipment of a typical double frequency receiver station
GPS-Receiver 4000SSE Trimble
GPS-Antenna Trimble
Meshnode
Meshnode Power Supply
electr. Accessories (Cable, plugs…)
Meshnode WLAN Antenna
2 Batteries (60Ah)
2 Solarpanels 50 Wp
Mountings for Solarpanel
Steel Pipe (3m)
Steel Pipe (2m)
Device Box
- Fig. 2.3 Setup of the IBIS station.
- Fig. 2.4 IBIS-L operating inside the wooden shelter.
- Fig. 2.5 IBIS-L moves on a rail behind the plexiglas-pane.
2.2 Installation of the IBIS-Station
Figure 2.3 provides an overview of the setup of the IBIS-L station.
2.2.1 Installation of IBIS-L
The microwave instrument IBIS-L, as provided by the manufacturer IDS, basically consists of the linear rail with a sled, the Radar sensor head with antennas, the power module including batteries and a Panasonic laptop for instrument control.
The installation of IBIS-L was done according to the installation guide provided by the manufacturer IDS. The first step is the construction of a concrete foundation and a wooden shelter. The concrete foundation must have a size of approximately 0.5 x 2.0 x 0.5 m. The rail is mounted on the concrete foundation by a fixture system composed of five thread rods, a reference sphere in the center of the rail and a positioning fork. In the front wall of the shelter, a Plexiglas pane of size 0.5 x 2.5 x 0.01 m was installed to protect the instrument from vandalism and weather. To reduce the multipath-effect, triggered by the Plexiglas, a shield of absorbing material was placed around the antennas of IBIS (see Figure 2.4).
Figure 2.5 shows the look from the outside into the wooden shelter. The two little orange squares are the radar-antennas of IBIS-L, moving along the 2m rail. In the back the processing laptop is visible.
2.2.2 Auxiliary equipment
For the purpose of data correction and understanding, a weather station for monitoring temperature, humidity and pressure and a webcam were installed at the station. The data gathering was done by a second laptop, which was also responsible for processing the IBIS-L data and communicating with the meshnode next to the IBIS station. To save and back up the data, two 1 TB external disk drives were used.
2.2.3 Power supply
For power supply eight 120 Wp solar panels were mounted on the roof and connected to the solar input of the IBIS-L power box. In case of cloudy weather, four 12 V, 70 Ah batteries can provide power for approximately 1.5 days.