## 5 Arctic-Based Field Observations  
The Arctic is a polar region located at the northernmost part of Earth. The Arctic region is a unique area among Earth's ecosystems. The cultures in the region and the Arctic indigenous peoples have adapted to its cold and extreme conditions. This region is also notably susceptible to climate change phenomena, which directly affect components of the environmental ecosystem. The impacts of climate change are seriously observed in the Arctic, and with more immediate and severe consequences than in most parts of the world. Field observations indicate that the Arctic is warming at almost twice the rate of the global average. Furthermore, reductions in sea ice and changes in weather are continuously visible. In the past decade, various measurements have been conducted--i.e., observation of carbon cycle and methane production, mapping of sea surface temperature, and measurement of ice extent. In 2010, [PERSON] and [PERSON] [95] performed a series of estimations of biomass and primary production (PP), which was measured by H14 CO3 uptake during in situ incubation. Active remote sensing was deployed in the research by using spaceborne LIDAR to provide information on the distribution of particles in the water column. In 2012, [PERSON] et al. [96] deployed research to validate the performance of the Arctic satellite, which observes sea surface temperature. Several sensors are considered in this work, which concluded that the AVHRR (NAVO-GAC) and the AATSR produce satisfactory results with very small bias. Additionally, it was noted that the amount of synchronized data validation of the AMSR-E is very high. A follow-up observation of the high-Arctic wet tundra area was extended by [PERSON] et al. [97]. In this research, methane (CH4) fluxes were observed using the in situ measurement method. A laser off-axis integrated cavity output spectroscopy analyzer was deployed to measure chamber concentration. The issue of global warming in the Arctic region was intensely studied by [PERSON] et al. [98] as the summer-time energy exchange characteristics were spotted and found to cause high sensible heat flux (H)/net radiation (\(Rn\)) and \(\beta\) and low latent heat flux (LE)/net radiation (Rn). In later years, dedicated research to observe the annual balance of CO2 and CH4 fluxes in the Arctic environment was performed by [PERSON] et al. [99]. Sensor performance was addressed by assessing sensor combinations on fluxes with different instrumentation at the same sites. Besides atmospheric conditions, concern regarding the Arctic sea ice extent has been addressed, as a reduction in volume is expected with increasing environmental temperature. [PERSON] et al. [100] re-calibrated the ice dataset using satellite sensing, as before the satellite era, geopolitical considerations were also a problem for the compilers of datasets. According to this research, the sea ice trend since the 1970s has been similar to the trend of ice growth after the mid-1940s. Other research addressed aerosol process and emission modeling, in which measurement of aerosol optical depth (AOD) is the critical  
Figure 16: (**a**) The acoustic emission sensor and (**b**) the model of the thyristors in plastic (**left**), stud-mount (**middle**), and press-pack packaging (**right**) [93]. process. Such research was conducted by [PERSON] et al. [101] using sun photometry and sky radiometry instrumentation. The data modeling was based on the input retrieval from the three AEROCAN sites (AEROCAN is the Canadian federated sub-network of AERONET). Later, an observation on ice melting was re-conducted, but in a more specific area. [PERSON] et al. [102] considered the Arctic region near Canada and Greenland for their work. Sentinel and synthetic aperture radar (SAR) were deployed for melt onset detection as two collaborating instruments in the observation.