  Internet of Things (IoT) applications are emerging in many different areas,
including maritime environments. One of the applications in this area is the
monitoring of buoys at sea. To realize wireless tracking of buoys, an accurate
prediction of the path loss in an open-sea environment is essential. So far,
channel measurements at sea have mainly been conducted with antennas placed a
couple of meters above the sea surface, which is higher than the buoys
themselves. Therefore, we investigated the validity of the published channel
models at sea by means of path loss measurements using a LoRa link with a
transmitter antenna height of 0.35 m and a base station antenna height of 2.65
m and 5.2 m. Our results show that the round earth loss model is not accurate
at these antenna heights. The ITU-R P.2001-3 model and a model by Bullington
show a better agreement with our measurements. However, the difference between
our two measurement campaigns shows that more investigation is needed on the
dependence of the path loss on the sea state. Additionally, the availability of
Sigfox, Narrowband Internet of Things (NB-IoT), and The Things Network at sea
has been explored. We found that NB-IoT and Sigfox can be used for IoT
applications in the tested area at low antenna heights.
