## 2 General Design and Features of the Instrument v2021
### Total Cost and Assembly Process  
The total bill of materials is presented in Table 2. We consider that around 0.5 h of work is needed to assemble a single instrument. No advanced electronics or hardware experience is required to build the instrument. At present, the assembly relies on a couple of soldering steps to connect the power supply module to the main board, and simply \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Activity Mode** & **Activation Frequency** & **Current (mA)** & **mWh Use per Hour** & **Time to Empty 2 Li D-Cells** \\ \hline sleep & when not active & 0.3 & 1.0 & 7.3 years \\ gnss measurement & 2 min twice per hour & 30 & 3.3 & 2.2 years \\ wave measurement & 20 min every 2 h & 8 & 4.4 & 1.6 years \\ iridium transmission & 1 message per hour & burst 250 mA & 10 & 0.7 years \\ typical use & & & 18.7 & 0.39 years \(\approx\) 4.6 months \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Overview of the power consumption and resulting battery autonomy resulting from the different components of the instrument when using two nonrechargeable D-sized Lithium batteries. ‘Activity mode’ indicates the part of the workflow of the instrument that is being considered. ‘Activation frequency’ indicates a typical activation duration and frequency (though this is only indicative and may be modified either by using different parameters when programming the instrument, and/or by sending updated activity rates through the bidirectional iridium communication). ‘Current (mA)’ is the average current used in the corresponding mode when it is active. ‘mWh use per hour’ indicates the corresponding energy use for the given activation mode, following the formula \(\text{mWh Use Per Hour}=\text{Current (mA)}\times 3.3\text{ (V)}\times\text{ActivationFraction}\). plugging the 9-dof sensor and the electronic switch controlling it into the main board using a couple of Qwic I2C cables. The total weight of the instrument depends on the size of the enclosure and the number of battery cells used. Typical weight is between 0.3 and 0.5 kg with 2 lithium D-cell batteries. The dimensions of the instrument are typically around 12 cm \(\times\) 12 cm \(\times\) 9 cm. Many of these parameters are part of design trade-offs. For example, more batteries increase weight and would make deployment from drones more challenging, but also allow to extend battery time. The use of a small enclosure allows for easier shipping and logistics and makes the instrument less likely to be discovered (and destroyed) by polar bears (in the Arctic), but means that even a relatively minor snowfall is enough to bury the instrument and interrupt GNSS and Iridium signals. In addition to the construction costs, Iridium costs can be significant over time. Table 3 indicates the typical Iridium communication costs per month, for an instrument running with the default parameters (reducing the frequency of measurements will reduce costs accordingly). Combining the building and the Iridium costs, the total cost per instrument, for an activity period of 6 months (which is reasonable for instruments deployed in the MIZ at the start of the ice formation season), is around 1200 USD, all included (noting that 4, rather than 2, LSH20 batteries will be necessary for such a deployment). Around 53% of this cost comes from the Iridium transmission fees; so, reducing the frequency of measurements