An investigation of low volume ag sensor data transmission using low-power transmission direct to Low Earth Satellite was completed in an under-graduate Engineering Honours project.  This project had a focus on the Australian developed and owned Myriota technology that provides data capture, storage, and transmission on roughly four hourly basis for less than $500 per transmitter unit.  Transmission of signals from the soil surface through crop canopy was tested using an analogue to the ~400 MHz transmission capability of this satellite technology.

To hasten in-field testing, over 800 test transmissions in the 900 MHz transmission range were completed between two transceivers using 2dB gain antennae from ground-to-ground points, and from ground to UAV.  Down-row, cross-row, and down-skip line-of-sight transmissions were measured and the transmission metrics of Returned Signal Strength Indicator (RSSI), Signal -to-Noise-Ratio (SNR), and Transmission-Success-Rate (TSR%) were calculated using averages of 20 results gathered at various distances. RSSI reduction at 100 metres was roughly 100 dB in all three ground-to-ground test directions using these extremely low capability antennae. SNR dropped to poor negative values between 50 and 100 metres. TSR% values dropped below 25% for the down-skip measurements and averaged 12% across crop rows, for the 100 metre test distance. For ground-point to UAV transmission simulating direct to satellite transmissions, ground angle increases from 0° to 20° improved RSSI by 35 dB, and no significant further increase occurred with higher simulated satellite positions. 

Two published empirical models for attenuation of Line-of-Sight radio signals were tested using this data, and an improved predictive model of signal loss through vegetation was developed.  Root-Mean-Squared-Error measures of the predictive capability of the new model averaged 6 dB for through vegetation, and were less than 10 dB for low ground angles to satellite