208 
P. Poli et al.: SVP-BRST: genesis, design, and initial results 
Ocean Sci., 15,199-214, 2019 
www.ocean-sci.net/15/199/2019/ 
Table 4. Similar to Table 1 but for two prototype SVP-BRST buoys (each buoy is fitted with a HRSST and static pressure probe). 
WMO identifier 
Deployment basin 
HRSST sensor model and S/N 
Start date 
End date 
6102622 
Mediterranean Sea 
Digital MoSens 4658 
26/04/2018 
12/06/2018 
6102623 
Mediterranean Sea 
Digital MoSens 4656 
26/04/2018 
- 
Figure 6. Sketch of the SVP-BRST (for the drogue, only the tether 
attachment is shown here), with the HRSST sensor unplugged 
shown in zoom panel (b). Note each SST sensor is protected from 
solar radiation by a cap. 
for investigation. Furthermore, the distribution of SST ob 
served within the 5 min is transmitted at coarse resolution 
(10th percentile, 30th percentile, 50th percentile or median, 
70th percentile, and 90th percentile). This non-parametric in 
formation makes no assumption about the shape of the SST 
distribution: it can be used to drive an ensemble of applica 
tions, rather than using solely the mean SST, and to assess, 
for example, whether the SST distribution is symmetric. 
Second, the HRSST sensor is removable from the buoy 
with simple tools (see Fig. 6), and includes a co-located pres 
sure sensor that allows reporting static pressure with an ac 
curacy of 5 cm in calm waters. Even if the instrument is af 
fected by accelerations in wavy conditions, and the depth is 
only valid in rather calm conditions (when the sensor depth is 
already known by design), information can be derived about 
the hydrostatic water pressure variability (within 5 min). 
Third, all SST sensors are insulated to shield them from 
unwanted effects caused by the non-water surrounding envi 
ronment. This aims to avoid, for the SST sensors, exchanges 
by conduction with the buoy hull, exchanges by radiation 
with the Sun and the atmosphere, and radio interference from 
the buoy electronic board and antenna. This is done in prac 
tice by using, respectively, insulating material between the 
sensor and the buoy, a small cap to shield the SST sensor 
from radiation, and a metal plate underneath the buoy elec 
tronic board and antenna. 
Fourth, the HRSST sensor is defined with a calibrating 
housing and protocol. Calibration coefficients are determined 
for each HRSST sensor individually so that their expanded 
calibration uncertainty can be assessed. These uncertainties 
are calculated according to the Guide For Uncertainty of 
Measurement (BIPM, 2008). They are found to be smaller 
than 0.01 K for each buoy. Response time and systematic er 
rors related to the integration in the buoy have been assessed 
on two prototypes. The details of these laboratory measure 
ments will be the subject of another paper. 
4 Results 
Initial testing was conducted in the Brest area (see the Sup 
plement). The results presented hereafter are based on data 
collected by the two prototypes in the Mediterranean Sea be 
tween 27 April and 11 June. The data are available in open 
access (see the section on data availability). 
4.1 Deployment 
Two SVP-BRST prototypes were deployed, as shown in Ta 
ble 4. At the time of writing, the second prototype is still 
operating. Before deployment for release, the buoys were 
deployed briefly on 23 April for comparison in the seawa 
ter with an SBE-35 thermometer. The SST differences were 
then found to be —0.006 K for one buoy and —0.001 K for 
the other buoy, thereby meeting the 0.01 K claimed uncer 
tainty. In comparison, the SST difference between the regu 
lar (or analogue) SST sensor with the SBE-35 was found to 
be — 0.05 K (for both buoys). 
4.2 Analysis of the data collected at sea 
Once deployed on 26 April 2018, the buoys have followed 
the tracks shown in Fig. 7. The separation distance between 
the two buoys, initially under 1km, remained under 10 km 
until 23 May. After that, the two buoys quickly diverged until 
the first one ran ashore. 
The buoy reports data to shore using Iridium according to 
a binary data format number no. 091 documented by Blouch 
et al. (2018). Besides the usual parameters reported by SVP- 
B buoys (position, time, strain gauge, air pressure, analogue 
SST, and other technical parameters such as battery voltage 
and GNSS TTFF), one notes the following key additions: the