The degradation of subarctic peatland ecosystems under climate change impacts surrounding landscapes, carbon balance, and biogeochemical cycles. To assess these ecosystems' responses to climate change, it is essential to consider not only the active-layer thickness but also its thermo-hydraulic conditions. Ground-penetrating radar is one of the leading methods for studying the active layer, and this paper proposes systematically investigating its potential to determine the thermal properties of the active layer. Collected experimental data confirm temperature hysteresis in peat linked to changes in water and ice content, which GPR may detect. Using palsa mires of the Kola Peninsula (NW Russia) as a case study, we analyze relationships between peat parameters in the active layer and search for thermal gradient responses in GPR signal attributes. The results reveal that frequency-dependent GPR attributes can delineate thermal intervals of +/- 1 degrees C through disperse waveguides. However, further verification is needed to clarify the conditions under which GPR can reliably detect temperature variations in peat, considering factors such as moisture content and peat structure. In conclusion, our study discusses the potential of GPR for remotely monitoring freeze-thaw processes and moisture distribution in frozen peatlands and its role as a valuable tool for studying peat thermal properties in terms of permafrost stability prediction.

Geogrid is widely used in slope, retaining wall, embankment, and other projects as the new geosynthetic material. In order to master the deformation behavior of geogrid, this study employs advanced optical frequency domain reflectometry (OFDR) technology to capture the deformation of geogrid; the optical fiber sensor installation method is considered; the influence of colloidal layer on strain transmission is explored; the medium type around the geogrid is changed; and the deformation characteristics of geogrid during the pulling process are analyzed. The results reveal that the strain of slotted layout is larger compared with tie layout, and the deformation trends of the two layouts are the same. The colloidal layer demonstrates an excellent strain transfer efficiency, with a coefficient of 97%. The geogrid pulling test successfully measures the deformation of geogrid in both sand and air medium using OFDR technology. The strain of the geogrid in sand medium is small; it indicates that the surrounding medium effectively restrains the deformation of geogrid.

The freeze-thaw (F/T) process plays a significant role in climate change and ecological systems. The soil F/T state can now be determined using microwave remote sensing. However, its monitoring capacity is constrained by its low spatial resolution or long revisit intervals. In this study, spaceborne Global Navigation Satellite System-Reflectometry (GNSS-R) data with high temporal and spatial resolutions were used to detect daily soil F/T cycles, including completely frozen (CF), completely thawed (CT), and F/T transition states. First, the calibrated Cyclone Global Navigation Satellite System (CYGNSS) reflectivity was used for soil F/T classification. Compared with those of soil moisture active and passive (SMAP) F/T data and in situ data, the detection accuracies of CYGNSS reach 75.1% and 81.4%, respectively. Subsequently, the changes in spatial characteristics were quantified, including the monthly occurrence days of the soil F/T state. It is found that the CF and CT states have opposite spatial distributions, and the F/T transition states distribute from the east to the west and then back to the east of the Qinghai-Tibet Plateau, which may be due to varying diurnal temperatures in different seasons. Finally, the first day of thawing (FDT), last day of thawing, and thawing period of the F/T year were analyzed in terms of the changes in temporal characteristics. The temporal variation of thawing is mainly different between the western and eastern parts of the Tibetan Plateau, which is in agreement with the spatial variation characteristics. The results demonstrate that the CYGNSS can accurately detect the F/T state of near-surface soil on a daily scale. Moreover, it can complement traditional remote sensing missions to improve the F/T detection capability. It can also expand the applications of GNSS-R technology and provide new avenues for cryosphere research.

针对美国地区6个GPS观测站5年（2012—2016年）的信噪比（signal to noise ratio,SNR）数据，利用GPS多径反射（GPS-multipath reflectometry,GPS-MR）方法详细分析了信号频率以及测站周围环境对雪深反演结果的影响，并与实测结果进行对比，讨论了该方法探测雪深的精度。结果表明，不同频率的SNR数据对反演精度影响不大，但会造成反演结果与真值之间存在一个系统偏差（频率L1的系统偏差约为0.1 m，频率L2C的系统偏差约为0.2 m）。地形起伏和其他物体遮挡均会影响反演精度，遮挡物较大甚至会造成反演失败。受积雪融化的影响，反演结果下降时间会较实测结果下降时间有所提前，致使两者之间的相关性降低。

针对美国地区6个GPS观测站5年（2012—2016年）的信噪比（signal to noise ratio,SNR）数据，利用GPS多径反射（GPS-multipath reflectometry,GPS-MR）方法详细分析了信号频率以及测站周围环境对雪深反演结果的影响，并与实测结果进行对比，讨论了该方法探测雪深的精度。结果表明，不同频率的SNR数据对反演精度影响不大，但会造成反演结果与真值之间存在一个系统偏差（频率L1的系统偏差约为0.1 m，频率L2C的系统偏差约为0.2 m）。地形起伏和其他物体遮挡均会影响反演精度，遮挡物较大甚至会造成反演失败。受积雪融化的影响，反演结果下降时间会较实测结果下降时间有所提前，致使两者之间的相关性降低。

针对美国地区6个GPS观测站5年（2012—2016年）的信噪比（signal to noise ratio,SNR）数据，利用GPS多径反射（GPS-multipath reflectometry,GPS-MR）方法详细分析了信号频率以及测站周围环境对雪深反演结果的影响，并与实测结果进行对比，讨论了该方法探测雪深的精度。结果表明，不同频率的SNR数据对反演精度影响不大，但会造成反演结果与真值之间存在一个系统偏差（频率L1的系统偏差约为0.1 m，频率L2C的系统偏差约为0.2 m）。地形起伏和其他物体遮挡均会影响反演精度，遮挡物较大甚至会造成反演失败。受积雪融化的影响，反演结果下降时间会较实测结果下降时间有所提前，致使两者之间的相关性降低。

Ground surface elevation changes are closely linked to the dynamics of the active layer and near-surface permafrost. GNSS interferometric reflectometry (GNSS-IR), a technique utilizing reflected signals regarded as noise in the GNSS applications, such as positioning and navigation, can measure surface elevation changes in permafrost areas. In this study, we screen seven major open-data GNSS networks to identify the sites which are suitable for using GNSS-IR to study the permafrost areas in the Arctic. We identify 23 usable sites and obtain their surface elevation changes. As for the unusable sites in the permafrost areas, 68% and 25% of them are due to undulated reflecting surface and obstructions (e.g., buildings and trees), respectively. And 7% of the unsuitable sites are due to insufficient usable observations, though open and relatively smooth areas can be found in their surroundings. This study provides usable sites in the Arctic permafrost areas, which can fill some spatial gaps of the existing permafrost monitoring programs and provide complementary measurements to active layer thickness and permafrost temperature. The GNSS-IR measurements can provide new perspectives into permafrost studies and contribute to assessing the potential hazards of permafrost degradation to infrastructures and residential communities.

Lunar Flashlight (LF) is an innovative National Aeronautics and Space Administration (NASA) CubeSat mission that is dedicated to quantifying and mapping the water ice harbored in the permanently shadowed craters of the lunar South Pole. The primary goal is to understand the lunar resource potential for future human exploration of the Moon. To this end, the LF spacecraft will carry an active multi-band reflectometer, based on an optical receiver aligned with four high-power diode lasers emitting in the 1 to 2-m shortwave infrared band, to measure the reflectance of the lunar surface from orbit near water ice absorption peaks. We present the detailed optical, mechanical, and thermal design of the receiver, which is required to fabricate this instrument within very demanding CubeSat resource allocations. The receiver has been optimized for solar stray light rejection from outside its field of view, and utilizes a 70 x 70-mm, aluminum, off-axis paraboloidal mirror with a focal length of 70 mm, which collects the reflected light from the Moon surface onto a single-pixel InGaAs detector with a 2-mm diameter, hence providing a 20-mrad field of view. The characterization of the flight receiver is also presented, and the results are in agreement with the expected performance obtained from simulations. Planned to be launched by NASA on the first Space Launch System (SLS) test flight, this highly mass-constrained and volume-constrained instrument payload will demonstrate several firsts, including being one of the first instruments onboard a CubeSat performing science measurements beyond low Earth orbit, and the first planetary mission to use multi-band active reflectometry from orbit.

Mapping and quantifying lunar water ice addresses one of NASA's Strategic Knowledge Gaps to understand the lunar resource potential for future human exploration of the Moon. Lunar Flashlight is an innovative NASA CubeSat mission dedicated to mapping water ice in the permanently-shadowed and occasionally-sunlit regions in the vicinity of the lunar South Pole. Lunar Flashlight will acquire these measurements from lunar orbit using a multi-band laser reflectometer composed of an optical receiver aligned with four lasers emitting different wavelengths in the shortwave infrared spectral region between 1 mu m and 2 mu m. The receiver measures the laser radiance reflected from the lunar surface in each spectral band and continuum/absorption reflectance band ratios are then analyzed to quantify water ice concentration in the illuminated spot. The receiver utilizes a 70x70-mm, aluminum, off-axis paraboloidal mirror with a focal length of 70 mm, which collects the incoming light onto a single, 2 mm diameter InGaAs detector with a cutoff wavelength of 2.4 mu m. We present the optical and mechanical designs of the receiver, including its optimization for rejection of solar stray-light from outside its intended field of view. This highly mass- and volume-constrained instrument payload will demonstrate several firsts, including being one of the first instruments onboard a Cube Sat performing science measurements beyond low Earth orbit and the first planetary mission to use multi-band active reflectometry from orbit.