# A New Orbiting Deployable System for Small Satellite Observations for Ecology and Earth Observation
## 3 Study Cases
### Application 2: Polynya Monitoring in Polar Areas  
Polynyas are open water or very thin layers of sea ice (with a threshold of ice content varying between 0.5 and 0.7, e.g., [116; 117]), which interpose the continuous ice blanket of the polar ice pack. They can be rectangular or oval shaped areas, reaching a size as large as 10 to \(10^{5}\) km\({}^{2}\) (e.g., [118]). Polynyas are quasi-permanent and highly dynamic, evolving through occasional openings and closings at the same location for up to several months, and they can reform over many years [119; 120; 121]. They can be formed by the combined influence of geological features, e.g., seamount, upwelling of warm water into the upper ocean from the thermocline (induced by a large cyclonic ocean eddy and negative wind stress curl), and large-scale anomalous atmospheric warming [122]. Polynyas, due to their nature, play a key role in regulating heat, energy, mass, and momentum exchanges between the ocean and the atmosphere, because they are openings in an otherwise solid ice pack, which performs as a barrier to hinder heat flows and to prevent ocean evaporation [123]. The monitoring of polynya dynamics in the polar regions represents an important science quest. Occurring in polar, mostly inaccessible areas, polynyas can benefit from remote sensing observations. On one side, passive microwave radiometers, such as the Advance Microwave Scanning Radiometer AMSR-E onboard the NASA/Aqua EOS satellite, are one of the most useful instruments to cover large areas without being affected by light conditions and cloud presence, but they suffer from a very coarse resolution (6.5 to 25 km), which prevents disentangling sea ice and open water areas, as well as the thin ice thicknesses [124]. On the other side, satellite thermal infrared imagery (TIR), such as that acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on the Aqua EOS satellite, has better resolutions (down to 1 km) and wider swaths than microwave radiometers, but it has the drawback effect of being sensitive to the cloud coverage [125]. SAR and optical sensors represent an alternative for both a better spatial resolution (down to 10-150 m) and for the possibility to be mounted in small platforms. TecSAR and DubaiSat-2 are examples of small satellites equipped with an X-band SAR [126] and an optical system in the VIS to NIR range [127], respectively. In addition, working in the microwaves, SARs are independent from atmospheric perturbations. Because their revisiting times (days to weeks) and swaths are unsuitable for the long-term continuous monitoring of phenomena occurring in polynyas [128], only constellations of satellites are adequate for monitoring polynya dynamics (e.g., Cappella X-SAR [57], Flock imaging constellation [129], and RapidEye [130]). Alternatively, the simultaneous use of complementary sensors (optical, thermal, and radar) has been thus suggested as the optimal approach for the long-term monitoring of polynyas, and/or the implementation of algorithms to strengthen the final output from the available data [124; 131; 132]. As, for instance, a multi-band TIR sensor, with at least two bands centered at about 11.0 \(\upmu\)m and 12.0 \(\upmu\)m, would be feasible to investigate polynyas [124; 131]. Temperatures measured at different TIR provide the ice surface temperature (IST), i.e., the sea ice surface temperature, which is fundamental in monitoring the periods of ice blanket opening and closing and its production curve in the polar regions [133; 134]. To determine IST value and polynya extent, a minimum revisiting time of 12 h, a swath of about 100 km, a minimum spatial resolution of about 500 m at nadir, and a noise-equivalent temperature difference (NEAT) of 0.05 K, are required. This observation strategy would overcome the current space and time resolutions of the existing satellite performances that are limiting the monitoring of polynya.