Integration of Smartphones Into Small Unmanned Aircraft Systems to Sense Water in Soil by Using Reflected GPS Signals

Abstract

We investigate the feasibility of using built-in GNSS sensors within ubiquitous smartphone devices from a small UAS for the purpose of land remote sensing. We summarize the experimental findings and challenges that need to be resolved in order to perform the GNSS Reflectometry (GNSS-R) technique via smartphones. In late 2018, a series of experiments was conducted and designed by integrating two smartphones into a multi-copter UAS by attaching them to ground plates to isolate and record both direct and reflected GNSS carrier-tonoise density ratio (C/N0) separately. It was demonstrated that (1) fluctuations of moving GNSS specular reflections are correlated with spatial ground features with appreciable dynamic range and (2) radiation pattern of the smartphone's inbuilt antenna has a significant effect on the received signal strength. In 2020, more experiments were conducted to examine the quality of in-built chip and antenna of a smartphone with regard to the GNSS-R approach as well as the consistency of measurements. These follow-up experiments involved (1) placement of the smartphone on a pan-tilt mechanism on a tripod (2) formation flights with smartphone on a gimbal and a high quality custom-built dualchannel GNSS-R receiver, and (3) flying the UAS at different times of the day on two consecutive days. It was demonstrated that (1) the radiation pattern of smartphone's GNSS antenna are observed to be highly irregular, but time-invariant, and (2) internal GNSS chip produces observables of sufficient quality, and (3) the fluctuations of the reflected signal are repeatable under the same configuration at different times.

A circularly polarized meander loop antenna for unmanned aerial vehicle satellite navigation system

“…Comparisons between the proposed antenna and other reference antenna designs for UAV applications are given in Table 1 , where λg is the guided wavelength of the antenna medium. As the navigation satellite signal is of CP senses, the ones reported in References 5, 6, 8 will exhibit a polarization loss factor equal to 0.5 because they are LP antennas. This causes the LP antenna built on the UAV to receive only half of the power transmitted by the satellite's CP antenna.…”

“…The applications of unmanned aerial vehicles (UAV) are becoming very popular in recent years as they can be used for military and civilian purposes. In military applications, UAVs can be used for training, reconnaissance, logistics, and combat 1 ; for civilian purposes, the typical applications include traffic monitoring, 2 precision agriculture, 3 infrastructure measurement, 4 tracking and surveillance, 5 scientific research, 6 search and rescue, 7 and so on. Depending on the purpose of the UAV, different equipment or sensors may be installed, or different communication frequency bands may be used.…”

GNSS Reflectometry-Based Ocean Altimetry: State of the Art and Future Trends

“…Several works have proven the efficiency of GPUs in GNSS-R receivers. It should be noted that mobile phones can also be receivers to sense water and soil via GNSS-IR [41,105,106].…”

Multilayer Model in Soil Moisture Content Retrieval Using GNSS Interferometric Reflectometry

“…Two smartphones were connected to the upper and lower sides of the plane, allowing for the isolation and recording of the direct and reflected GNSS carrier noise density ratios as well as the remote sensing of land surface data. The results revealed that the reflected signals exhibited geographical correlations in line with surface properties, including the pond’s high reflectivity, susceptibility to different types of land crops, and soil wetness [ 20 ]. When an electromagnetic wave shines on a dielectric material—that is, when it passes through the upper dielectric and is reflected by the lower dielectric—it exhibits the phenomena of the complete transmission.…”