Lake ice is an important variable in cryospheric hydrology that is quite sensitive to climate change, serving as a regulator to regional climate as well as lake ecosystems and a natural resource to sustain human activities on the ice. Lake ice cover and Lake Ice Thickness (LIT) are two key variables in lake ice studies. However, most lake ice studies focus on lake ice cover as opposed to LIT, due mostly to the lack of in situ LIT observations and effective satellite platforms. Consequently, LIT states in ungauged basins remain largely unknown, and critical knowledge gaps need to be filled with breakthroughs in remote sensing observations and retrieval methods. This study reviews the progress in the remote sensing of LIT for the past two decades, focusing on methods based on active and passive microwave information as well as methods based on thermal infrared information. Currently, the best retrieval accuracy of LIT is 0.1—0.2 m for satellite platforms, unable to meet the accuracy requirement (1—2 cm) from the Global Climate Observing System (GCOS). Passive microwave sensors such as AMSR-E and AMSR2 with high temporal-resolution and coarse spatial resolution (~30 km) are efficient for monitoring LIT in large lakes. SAR images can be used to discriminate bedfast lake ice and floating ice, applicable to shallow lakes and lakes with bathymetry information. Waveforms of satellite altimeters containing signals backscattered from the lake ice surface and the lake ice bottom can be used to estimate the traveling time of radar pulse within the ice, which is suitable for ungauged basins because the method is physically based and does not need calibration. Backscattering coefficients from satellite altimeters can also reflect LIT evolution but needs further investigation to improve its robustness. Thermal infrared information such as MODIS land surface temperatures can be used to drive lake ice models to estimate the LIT, but its accuracy is subject to the complicated process of lake surface snow. We summarize the challenges for current LIT studies and indicate future directions for LIT studies. There are four critical issues: (1) The physical process of lake ice and lake surface snow needs to be better resolved to improve the performance of remote sensing and modeling of LIT; (2) In situ measurements of LIT need to be aggregated and standardized in a larger scale to provide sufficient calibration and validation data; (3) Multisource remote sensing information of LIT can be better combined with lake ice modeling through data fusion and data assimilation to derive global LIT datasets with a longer period, higher spatiotemporal resolution and better accuracy; (4) With the development of new generations of satellite platforms, such as the latest altimetry missions (e.g., ICESat-2, Jason-CS, and SWOT) and SAR platforms, advanced methods can be developed to better achieve the LIT monitoring target set by GCOS.

lake ice thickness;brightness temperature;Backscattering coefficient;satellite altimetry;thermal infrared remote sensing