Land Cover Mapping in Northern High Latitude Permafrost Regions with Satellite Data: Achievements and Remaining Challenges

Abstract

Most applications of land cover maps that have been derived from satellite data over the Arctic require higher thematic detail than available in current global maps. A range of application studies has been reviewed, including up-scaling of carbon fluxes and pools, permafrost feature mapping and transition monitoring. Early land cover mapping studies were driven by the demand to characterize wildlife habitats. Later, in the 1990s, up-scaling of in situ measurements became central to the discipline of land cover mapping on local to regional scales at several sites across the Arctic. This includes the Kuparuk basin in Alaska, the Usa basin and the Lena Delta in Russia. All of these multi-purpose land cover maps have been derived from Landsat data. High resolution maps (from optical satellite data) serve frequently as input for the characterization of periglacial features and also flux tower footprints in recent studies. The most used map to address circumpolar issues is the CAVM (Circum Arctic Vegetation Map) based on AVHRR (1 km) and has been manually derived. It provides the required thematic detail for many applications, but is confined to areas north of the treeline, and it is limited in spatial detail. A higher spatial resolution circumpolar land cover map with sufficient thematic content would be beneficial for a range of applications. Such a land cover classification should be compatible with existing global maps and applicable for multiple purposes. The thematic content of existing global maps has been assessed by comparison to the CAVM and regional maps. None of the maps provides the required thematic detail. Spatial resolution has been compared to used classes for local to regional applications. The required thematic detail increases with spatial resolution since coarser datasets are usually applied over larger areas covering more relevant landscape units. This is especially of concern when the entire Arctic is addressed. A spatial resolution around 30 m has been shown to be suitable for a range of applications. This implies that the current Landsat-8, as well as Sentinel-2 missions would be adequate as input data. Recent studies have exemplified the value of Synthetic Aperture Radar (SAR) in tundra regions. SAR missions may be therefore of added value for large-scale high latitude land cover mapping. Remote Sens. 2016, 8, 979 2 of 27with climate change in the upcoming decades [2]. It has been pointed out by a range of studies (e.g., Westermann et al. [1] and Ottle et al. [3]) that there is a need for accurate land cover description in the northern high latitudes. A suitable circumpolar map does not yet exist to date, although a range of studies demonstrated the suitability of satellite data for this purpose on local and regional scales.A first review on traditional Arctic land cover maps as a baseline for the development of a circumpolar map was already published in 1995 by Walker et al. [4]. The Circum-Arctic Vegetation Map (CAVM) has in the following been developed using satellite data (Advanced Very Hi...

Simplified Normalization of C-Band Synthetic Aperture Radar Data for Terrestrial Applications in High Latitude Environments

“…They vary regarding heterogeneity (abundance of lakes), vegetation and soils. All regions are areas with past and ongoing research studies linked to land cover [15]. Topographic gradients and mean number of tracks are provided in Table 1.…”

“…In these studies a pixel based approach for normalization was chosen and the linear model derived for the Arctic studies [13,14] based on an average of 46 ASAR GM acquisitions per location. ASAR GM does however only provide 1 km spatial resolution and higher spatial resolution is needed in order to capture the heterogeneity of Arctic environments [15]. It has been demonstrated that applications developed for GM can be transferred to data from ASAR operating in Wide Swath (WS) mode (150 m) and they can provide much higher detail and actual landscape patterns [14].…”

Upscaling CH4 Fluxes Using High-Resolution Imagery in Arctic Tundra Ecosystems

“…Mapping arctic tundra vegetation is very challenging due to the enormous heterogeneity present over a few meters ( [39,43,84]. Not only can the variability of the vegetation make mapping more difficult, but the substantial cloud cover in the Arctic can decrease the number of available images that can be used for this excersise [85].…”

“…Other data products, such as aerial imagery obtained through the use of drones or LiDAR-derived digitial elevation models (DEMs), could be used to resolve this issue [86,87] as they could also account for variability within the local microtopography. However, Bartsch et al [43] note that even coarse resolution maps can have value, especially in carbon/upscaling studies, and drones or LiDAR-derived digitial elevation models (DEMs) are expensive to collect and cannot be easily collected over large areas.…”

“…These sensors' data can capture fine spatial scale vegetation community distribution, something which coarser products such as AVHRR or Landsat cannot [42]. On the other hand, WorldView-2 data are limited in temporal resolution [43] and the acquisition cost, limiting the ability to capture the short and fast phenological dynamics across the tundra [41], which can greatly contribute to the dynamics of CH 4 consumption and production. However, in polygonal tundra ecosystems with substantial spatial heterogeneity, they might be the only products that allow the capturing of small scale variability in vegetation controls on CH 4 fluxes across the eddy covariance tower footprint.…”