Development and analysis of a continuous record of global near-surface soil freeze/thaw patterns from AMSR-E and AMSR2 data

Abstract

Abstract. Monitoring near-surface soil freeze/thaw patterns is becoming essential under the context of global changes as it is more sensitive to climatic fluctuation compared with subsurface thermal characteristics and its 15 evolution could be an early warning of changes in near-surface permafrost. It requires continuous long term and stable data record for understanding hydrological, ecological and biogeochemical responses of permafrost to global climate change. AMSR2 (Advanced Microwave Scanning Radiometer 2) is designed as a successor of AMSR-E (Advanced Microwave Scanning Radiometer -Earth Observing System) to ensure continuity of such observation.In this study, a linear regression is used to inter-calibrate the AMSR-E and AMSR2 brightness temperatures. Then 20 discriminant function algorithm is adopted to produce a long term freeze/thaw data record. It is compared with in situ air temperature measurements from both the temporal and spatial aspects. The results show that the accuracy is consistent between AMSR-E and AMSR2 with a value above 85%, according to the result of spatial distribution accuracy. Analysis is conducted with this data record to explore the spatial distribution of frost days, its changing trend and the frost probability of each pixel on a specific date. The mean annual frost days of high northern latitude 25 (HNL, >45°N) zone is 214.2±69.5 days and the trend of frost days indicates that the frost period is decreasing at a rate of -0.0065 day/month in 27% of the domain which is defined by significance level of the F-test, and most of which are concentrated in the high latitude area specifically over the Northeast of Canada, Central and Eastern Russia and most part of Eastern Europe. The significant changes in frost days mostly occur in regions of discontinuous permafrost and transient permafrost. The spatial distribution of the frost days and its trend variations 30 are found to be consistent with the minimum temperature anomalies trend. It indicates that the global warming is not constant at different regions over the globe. Further analysis over the Qinghai-Tibetan Plateau where discontinuous permafrost, island permafrost, seasonally frozen ground exist demonstrated that the frost period is shortening slightly over the past decade, and the last frost date is advanced over more than half of the region. It is considered to be a remarkable indication for permafrost degradation in this area.

High-Resolution Mapping of Freeze/Thaw Status in China via Fusion of MODIS and AMSR2 Data

“…It also has the highest accuracy compared with two other algorithms, dual index [9] and decision tree algorithm [11], when applied to AMSR-E data [22]. In addition, further validation of this algorithm was conducted in our previous work using in situ air temperature measurements from the World Meteorological Organization (WMO, 88.37% and 82.76% for observations at 1:30 and 13:30, respectively), 0-5 cm soil temperature from International Soil Moisture Network (ISMN, 86.63%), as well as modelled soil temperature by the Global Land Data Assimilation System (GLDAS, 89.74% and 87.6% for observations at 1:30 and 13:30, respectively) [23]. A brief introduction of DFA is presented here.…”

“…Although AMSR-E and AMSR2 have been reported to have slight differences [29,30], eliminating the difference is still necessary through inter-calibration before applying the same algorithm (e.g., DFA) to observations of these two sensors [31]. The data of AMSR2 used in this study have been calibrated with AMSR-E without many details being obtained [23]. The high-resolution F/T maps also depend significantly on thermal observations, especially the spatial resolution.…”

Estimation of high‐resolution near‐surface freeze/thaw state by the integration of microwave and thermal infrared remote sensing data on the Tibetan Plateau

“…A lot of studies have demonstrated that microwave remote sensing is feasible for freeze/thaw state estimation including passive and active sensors with various temporal and spatial resolutions. Space‐borne radiometers such as the scanning multichannel microwave radiometer (SMMR) [ Zuerndorfer and England , ], Special Sensor Microwave Imager (SSM/I) [ Judge et al , ; Jin et al , ; Kim et al , ], Advanced Microwave Scanning Radiometer–EOS (AMSR‐E) [ Zhao et al , ], and Advanced Microwave Scanning Radiometer 2 [ Hu et al , ] data have provided a way to produce a long‐term data record of near‐surface freeze/thaw state, since the availability of K a band allows these sensors to detect the surface temperature changes reliably. However, the indication for water phase transition of these sensors operating at C band or higher frequencies is weaker compared to the L band.…”