3 Software installation
The processing is done with commercial software: the Bernese Software for the GPS-data and the standard IDS software that comes with IBIS for the IBIS-data. The process controlling and the in-between data handling is carried out by Perl- and Python-Scripts, which are available from the link on the bottom. The detailed processing steps are explained below.
3.1 GPS Processing
3.1.1 Collecting GPS-data with meshnodes
On every GPS-station a meshnode controls the GPS-receiver, saves the data and establishs the WLAN-network to send the data to the central database. The meshnodes boot device and hard disk is an 8 GB compact flash card. The operating system is Linux (Ubuntu 8.04 Hardy Heron). An iso-image of a bootable compact flash card can be downloaded here.
All meshnodes are equipped with two WLAN-cards, they have to work in adhoc mode, so the meshing can be done with olsrd, an adhoc wireless mesh routing daemon (for more information about the meshing see WP4).
- Collecting data with a Trimble dual-frequency receiver
Every 10 minutes the perl-script log_sse.pl does the following:
1. start the receiver with the tool rstream and collect data for 10 minutes
(for the software see Trimble R-Utilities),
2. convert data with the Trimble R-Utilities-tools rt172dat and dat2rin into RINEX-format,
3. send RINEX-data via WLAN to the field-server, archive RINEX-data on local meshnode.
- Collecting data with an Antaris ublox single-frequency receiver
Every 10 minutes the perl-script log_ubx.pl does the following:
1. start the receiver with logserial, collect data for 10 minutes,
2. convert data with free_linux_RD2 into RINEX-format,
3. send RINEX-data via WLAN to field-server, archive RINEX-data on local meshnode.
- Fig. 3.1 Collecting Data with a Trimble Dual Frequency Receiver
- Fig. 3.2 Collecting Data with an ublox Receiver
3.1.2 GPS processing on the field-server
All collected field data is sent to the field-server. Here the RINEX-data is processed with the bernese software.
The perl script make_gps_xml.pl writes the coordinate changes with respect to the precedent epoch, as well as the coordinate changes with respect to a predefined epoch 0 and their standard deviations in an xml-file and sends it via WLAN to the database.
- Fig. 3.3 Realtime processing concept of IBIS-L data.
3.2 IBIS Processing
3.2.1 IBIS-L Controller
IBIS is controlled by the IBIS-L Controller Software provided by the manufacturer IDS which is installed on the Panasonic laptop. With the configuration used on the Azores (range 2000 m, maximum resolution), one file is stored on the Panasonic laptop every 10 minutes with a file size of 16 MB containing raw (unfocused) SAR data.
3.2.2 IBIS-L Processing
For near realtime processing of the IBIS-L data a Matlab script was written based on routines provided by IDS. The processing software was installed on the Dell laptop (Windows XP). The Panasonic and Dell laptops communicate via LAN. Fig. 3.3 shows the processing concept and file transfer. The first step of processing is the backup. The raw data are saved on both external disc drives and deleted on the Panasonic laptop. After that the raw data is focused. The focused file contains amplitude and phase information of each resolution cell.
The next steps are interferogram creation and computation of coherence. For that, at least two acquisitions have to be present. By using a Digital Elevation Model (DEM) the data is geocoded and exported as Geotiff. Additionally, the displacements are computed by applying atmospheric correction. The final Geotiffs are sent to the database via WLAN.
3.2.3 Automated startup
In case of power failure, the IBIS-L data acquistion stops and the laptops are shutdown. When power is reinstated, the Dell laptop is booting automatically (Power on AC). After booting successfully a script is launched to wake up the Panasonic laptop using its network card (Wake on LAN). The script can be found here.
- Fig. 3.4 Typical webcam image of the monitored area.
3.3 Auxiliary Data
3.3.1 Webcam
The Webcam images can be used to identify the reasons of strange displacement signals which might be caused by clouds or fog in front of the monitored area. Every ten minutes an image is saved by the use of a Java script which can be found here.
3.3.2 Meteorological Data
Temperature, humidity and pressure are observed and stored in a file every ten minutes. The data is read from the weather sensors by means of a Java script which can be found here.