September 2025 | Oceanography
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temporal resolution of current variability. However, increases in
drogue drag require a stronger, more robust structure, and a
potentially more complicated deployment due to size. All of these
considerations allow students to explore how different mechani-
cal designs affect the performance and ease of drifter deployment.
ELECTRONIC DESIGN: GPS TRACKERS
Each of our student teams received a commercial off-the-shelf
GPS communication system. This system transmits GPS data via
an LTE-M network, which uses the existing 4G LTE infrastruc-
ture to send data from Internet of Things (IoT) devices over a fre-
quency range of 700–1,200 MHz. Course staff provided the stu-
dents with a monthly subscription for the commercial tracker. To
increase the communication range, students were given the option
to replace the stock LTE antenna with a higher-gain directional
LTE antenna. They estimated the commercial GPS unit’s trans-
mission distance with and without the antenna modification and
found that the modified unit, with the directional antenna, offered
an estimated range of 10–15 km from a cell tower. The commercial
GPS is configured to transmit every 10 minutes, but this interval
may vary depending on the availability of both the GPS and the
LTE-M signals.
To further advance learning, student teams were also given the
option to implement a custom-built cellular communication sys-
tem. This setup allowed them to integrate additional environmen-
tal sensors, such as those for temperature and barometric pressure.
The custom tracker included: (1) an ESP32 board with a SIM7000G
GPS/cellular modem, (2) a 18650 lithium-ion battery, (3) GPS
and cellular antennas, (4) a global SIM card, and (5) optional
barometer and temperature sensors. The students practiced esti-
mating the operational time for the custom system based on their
choices for data sampling and transmission frequency. Figure 3
displays a block diagram of the code for the electronics.
The electronic stack was enclosed in a bamboo container coated
with water-resistant shellac resin (Figure 3). This housing was
designed to keep the electronics dry during splashing and brief
submersion, with the expectation that it would remain at least
10 cm above the waterline for most of the deployment. To improve
waterproofing, students could use coconut wax to protect elec-
tronics, excluding antennas.
FIGURE 3. (a) Electronic
system block diagram for
the drifter. (b) Tear down
of the commercial GPS
tracker electronics com-
ponent. (c) Custom GPS
tracker electronics com-
ponents. (d) Coconut wax
potting
example.
The
code for the custom GPS
is available on Github.