Abstract. Given the tradeoffs between spatial and temporal resolution, questions about
resolution optimality are fundamental to the study of global snow. Answers
to these questions will inform future scientific priorities and mission
specifications. Heterogeneity of mountain snowpacks drives a need for daily
snow cover mapping at the slope scale (≤30 m) that is unmet for a
variety of scientific users, ranging from hydrologists to the military to
wildlife biologists. But finer spatial resolution usually requires coarser
temporal or spectral resolution. Thus, no single sensor can meet all these
needs. Recently, constellations of satellites and fusion techniques have
made noteworthy progress. The efficacy of two such recent advances is
examined: (1) a fused MODIS–Landsat product with daily 30 m spatial
resolution and (2) a harmonized Landsat 8 and Sentinel 2A and B (HLS) product with
3–4 d temporal and 30 m spatial resolution. State-of-the-art spectral unmixing
techniques are applied to surface reflectance products from 1 and 2 to
create snow cover and albedo maps. Then an energy balance model was run to
reconstruct snow water equivalent (SWE). For validation, lidar-based
Airborne Snow Observatory SWE estimates were used. Results show that
reconstructed SWE forced with 30 m resolution snow cover has lower bias, a
measure of basin-wide accuracy, than the baseline case using MODIS (463 m
cell size) but greater mean absolute error, a measure of per-pixel
accuracy. However, the differences in errors may be within uncertainties
from scaling artifacts, e.g., basin boundary delineation. Other explanations
are (1) the importance of daily acquisitions and (2) the limitations of
downscaled forcings for reconstruction. Conclusions are as follows: (1) spectrally
unmixed snow cover and snow albedo from MODIS continue to provide accurate
forcings for snow models and (2) finer spatial and temporal resolution
through sensor design, fusion techniques, and satellite constellations are
the future for Earth observations, but existing moderate-resolution sensors
still offer value.