This document gives contextual information about the LoRa farm dataset.
Published July 2019
The underground nodes are using a high power LoRa module: HOPE Microelectronics RFM98PW-169S2 specified for operation at 169 MHz and tuned for 174 MHz with a power output of 100 mW according to frequency regulations. Power is supplied by 6 D cells through regulators (5 V for LoRa module and 3.3 V for Atmega328 microcontroller). The antenna is a quarter wave long (about 43 cm) and the corresponding ground plane provided by the alumina chassis of the printed circuit board. Due to the extension of the antenna only horizontal polarization is possible and the broadside of the structure has to direct to the receiver location. The antenna resonance is affected by the surrounding soil but minimized by a large diameter of the enclosure (about 10 cm) and a thick antenna element. The nodes transmit with the LoRa settings spreading factor SF9, bandwidth BW125 and coding rate CR4/5. Power is about 100 mW or 20 dBm at 174 MHz. The radio node provides an RS485 bus with switched power for sensors. A configurable number of precision soil water content and temperature sensors SMT100 (TRUEBNER) can be attached. The receiver is based on the same LoRa module connected to a ring dipole approximating an omni-directional radiation pattern. For redundancy and possible diversity reception two receiver systems are mounted on a metal tower in the field at an approximate height of 3 meters and oriented of 120 degrees to one another. One receiver is connected via USB to a Raspberry Pi and the other via RS485 to an Atmega328 controlled logger for storing data on flash memory. The data transmission scheme is transmit-only. Transmissions are schedules at regular intervals with a superimposed random time variation to decrease the probability of collisions with other radio nodes. The measurements (soil moisture and temperature) are extended with housekeeping data. A simple coding technique reduces the data size by combining blocks of two bytes of the original data (ASCII string with characters 0..9,+,-,.) into a single byte. Decoding is done in the receiver. Xtended Tiny Encryption Alogorithm (XTEA) can be optionally turned on.
Datasheets for the hardware are given in the references.
Moisture loggers/sensors deployed 10.09.2018
Station 1 (on top of hill near a dolorite dyke, lots of coarse fragments, red soil, clay rich) -32 30.430801 116 57.799640 There are 4 sensors Sensors 1, 3 are at 20 cm depth Sensors 2, 4, are in 40-50 cm depth
Station no 2 (next to flux tower soil moisture station, typical duplex Chromosol) 50H E 496738.4239 N 6403462.8996 There are 4 sensors Sensors 1, 3 are at 20 cm depth Sensors 2, 4, are in 40-50 cm depth
Station 3 (water logged during winter, clay rich – most challenging conditions for transmission) -32 30.212040 116 57.870930 There are 4 sensors Sensors 1, 3 are at 20 cm depth Sensors 2, 4, are in 40-50 cm depth
Station 4 (slightly elevated, typical duplex Chromosol) -32 30.340330 116 58.103150 There are 4 sensors Sensors 1, 3 are at 20 cm depth Sensors 2, 4, are in 40-50 cm depth
Station no 5 50H E 496821.7591 N 6403577.0190 There are 8 sensors each 10 m from the station in N-S-E-W arrangement Sensors 1, 3, 5, 7 are at 20 cm depth Sensors 2, 4, 6, 8 are in 40-50 cm depth
Ethics permission is not applicable for this dataset.
Node 4 was reset on 10 Ocotober. 11: 2018-10-16T08:48:11Z 1539679691 4 5210 -78 -85 12: 2018-10-16T09:46:29Z 1539683189 4 2 -75 -85
LoRa settings are ``over-engineered" for this prototype. In future it would be interesting to include some lower settings to assess the feasibility of low energy networks.
[UWA Farm Information]{http://www.science.uwa.edu.au/centres/land/ridgefield}
[Farm Weather Station]{http://www.ioa.uwa.edu.au/future-farm-2050/visiting-researching}
[Dept of Agriculture Weather Station]{https://weather.agric.wa.gov.au/} Station number PY001 Pingelly West weather station is only a few hundred meters away from the field site.
[RFM98PW] {https://www.hoperf.com/data/upload/portal/20190301/RFM98PW.pdf}
[ATmega328] {http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf}
[SMT100] {http://www.truebner.de/sites/default/files/SMT100_Flyer_A4_english.pdf}