Overview
The Moderate Resolution Imaging Spectro-Radiometer (MODIS) is carried on two NASA-operated satellites, Terra and Aqua. Both are in sun-synchronous, near-polar, circular low-Earth orbits at altitudes of 705 km. Terra, operational since 24 February 2000, crosses the equator ~10:30 (descending – travelling N to S) and 22:30 (ascending – travelling S to N) daily: Aqua, operational since 4 July 2002, crosses the equator ~13:30 (ascending) and 01:30 (descending) daily.

The sensor captures images in 36 spectral bands: two are at 250 m (nominal) spatial resolution, five at 500 m and the remainder at 1000 m. Its broad swath (field of view orthogonal to orbital track) of 2330 km ensures that the great majority of the Earth’s surface is imaged every day.

The MODIS snow-cover datasets infer the presence of snow based on the Normalized Difference Snow Index (NDSI), using the NASA VIIRS algorithm described in Hall et al. (2015 – available at
https://viirsland.gsfc.nasa.gov/PDF/VIIRS_snow_cover_ATBD_2015.pdf:
see also https://nsidc.org/support/faq/what-ndsi-snow-cover-and-how-does-it-compare-fsc).
NDSI is computed as (MODIS Band 4 - MODIS Band 6) / (MODIS Band 4 + MODIS Band 6)
where MODIS Band 4 detects wavelengths in the range 545 – 565 nm (green visible light) and MODIS Band 6 covers 1628 – 1652 nm (near infrared)
A range of pixel-level quality flags are also provided, from which it is possible to infer a qualitative degree of confidence in the estimated values.

Data products are as follows (comprehensive details are available from the links in the Link to download data section):

MODIS Terra / Aqua Snow Cover 5-Min L2 Swath 500m MOD10_L2 / MYD10_L2
Estimated percentage snow cover within pixel, inferred from NDSI
This dataset provides the basis for the Level 3 products described below
Each granule contains one scene, the full swath-width view acquired during five minutes of orbital travel
Nominal spatial resolution is 500 m at the nadir: referenced to the WGS84 datum (unprojected)

MODIS Terra / Aqua Snow Cover Daily L3 Global 500m SIN Grid MOD10A1 / MYD10A1
Estimated percentage snow cover within pixels, inferred from NDSI: albedo
Each granule is a 10°x10° tile projected onto a sinusoidal grid
Nominal spatial resolution is 500 m: true pixel dimensions are 463.313 m

MODIS Terra / Aqua CGF Snow Cover Daily L3 Global 500m SIN Grid MOD10A1F / MYD10A1F
As for MOD10A1 and MYD10A1, but with any cloud-obscured pixels filled using values from previous days. The dataset also provides the number of days between the granule’s nominal date and that on which the most recent unobscured view of each pixel was available.

MODIS Terra / Aqua Snow Cover 8-Day L3 Global 500m SIN Grid MOD10A2 / MYD10A2
Pixel values represent the maximum estimated percentage snow cover derived from MOD10A1 / MYD10A1 from granules observed over the prior eight days.

MODIS Terra / Aqua Snow Cover Daily L3 Global 0.05Deg CMG MOD10C1 / MYD10C1
Provides estimated percentage snow-covered area within 0.05° cells in the MODIS Climate Modelling Grid (CMG), computed from MOD10A1 / MYD10A1

MODIS Terra / Aqua Snow Cover 8-Day L3 Global 0.05Deg CMG MOD10C2 / MYD10C2
Pixel / cell values represent the maximum estimated percentage snow cover within 0.05° cells in the MODIS Climate Modelling Grid (CMG), derived from MOD10A1 / MYD10A2 from granules observed over the prior eight days.

MODIS Terra / Aqua Snow Cover Monthly L3 Global 0.05Deg CMG MOD10CM / MYD10CM
Pixel / cell values represent the monthly mean estimated percentage snow cover within 0.05° cells in the MODIS Climate Modelling Grid (CMG), derived from the corresponding MOD10C1 / MYD10C1 daily granules.

Provider contact information
Terra and Aqua platforms operated by NASA: data distributed by US National Snow and Ice Data Center (NSIDC) – https://nsidc.org

Licensing
See http://nsidc.org/about/use_copyright.html

Variable name and units
Principally, estimated percentage snow-covered area: MOD10A1 and MYD10A1 also provide albedo

Spatial coverage and resolution
All datasets provide global coverage

Nominal 500 m pixel-size, unprojected, referenced to WGS84 datum:
MODIS Terra / Aqua Snow Cover 5-Min L2 Swath 500m MOD10_L2 / MYD10_L2

Gridded in MODIS sinusoidal projection (true pixel dimensions are 463.313 m):
MODIS Terra / Aqua Snow Cover Daily L3 Global 500m SIN Grid MOD10A1 / MYD10A1
MODIS Terra / Aqua CGF Snow Cover Daily L3 Global 500m SIN Grid MOD10A1F / MYD10A1F
MODIS Terra / Aqua Snow Cover 8-Day L3 Global 500m SIN Grid MOD10A2 / MYD10A2

Upscaled to 0.05°cells within MODIS Climate Modelling Grid (CMG):
MODIS Terra / Aqua Snow Cover Daily L3 Global 0.05Deg CMG MOD10C1 / MYD10C1
MODIS Terra / Aqua Snow Cover 8-Day L3 Global 0.05Deg CMG MOD10C2 / MYD10C2
MODIS Terra / Aqua Snow Cover Monthly L3 Global 0.05Deg CMG MOD10CM / MYD10CM

Temporal coverage and resolution
Terra since 2000-02-24, Aqua since 2002-07-04

Information about related datasets
n/a

Limitations and strengths for application
- Daily return intervals are assured at high latitudes.
- Overlap in the sensor’s field of view at high latitudes also means that a greater fraction of the pixels in any given scene are observed at angles of view closer to nadir on any given day. The nadir along-track view covers 10 km per scene.
- Snow is not detected in pixels experiencing where the solar zenith angle at the time of image capture ≥ 85°: this includes Polar Night.
- The relationship between NDSI values and percentage now-cover was derived empirically – but this may not hold reliably in all contexts (e.g., as a result of the influence of topography, vegetation, clouds).

References
For product-specific details, see links provided below

Original introductory paper:
Hall et al. (2002) MODIS snow-cover products Remote Sensing of Environment 83(1–2), pp. 181-194
https://doi.org/10.1016/S0034-4257(02)00095-0

Guide to latest collection (Collection 6.1):
Riggs et al. (2019) MODIS Snow Products Collection 6.1 User Guide
https://modis-snow-ice.gsfc.nasa.gov/uploads/snow_user_guide_C6.1_final_revised_april.pdf

NASA overview of MODIS snow products
https://modis.gsfc.nasa.gov/data/dataprod/mod10.php

Link to download data (and format)
Distributed by the US National Snow and Ice Data Center (NSIDC) Distributed Active Archive Center (DAAC)
https://nsidc.org/data/MOD10A1/versions/6

MODIS Terra Snow Cover 5-Min L2 Swath 500m MOD10_L2
https://nsidc.org/data/MOD10_L2/versions/61
MODIS Aqua Snow Cover 5-Min L2 Swath 500m MYD10_L2
https://nsidc.org/data/MYD10_L2/versions/61

MODIS Terra Snow Cover Daily L3 Global 500m SIN Grid MOD10A1
https://nsidc.org/data/MOD10A1
MODIS Aqua Snow Cover Daily L3 Global 500m SIN Grid MYD10A1
https://nsidc.org/data/MYD10A1

MODIS Terra CGF Snow Cover Daily L3 Global 500m SIN Grid MOD10A1F
https://nsidc.org/data/MOD10A1F/versions/61
MODIS Aqua CGF Snow Cover Daily L3 Global 500m SIN Grid MYD10A1F
https://nsidc.org/data/MYD10A1F/versions/61

MODIS Terra Snow Cover 8-Day L3 Global 500m SIN Grid MOD10A2
https://nsidc.org/data/MOD10A2/versions/61
MODIS Aqua Snow Cover 8-Day L3 Global 500m SIN Grid MYD10A2
https://nsidc.org/data/MYD10A2/versions/61

MODIS Terra Snow Cover Daily L3 Global 0.05Deg CMG MOD10C1
https://nsidc.org/data/MOD10C1/versions/61
MODIS Aqua Snow Cover Daily L3 Global 0.05Deg CMG MYD10C1
https://nsidc.org/data/MYD10C1/versions/61

MODIS Terra Snow Cover 8-Day L3 Global 0.05Deg CMG MOD10C2
https://nsidc.org/data/MOD10C2/versions/61
MODIS Aqua Snow Cover 8-Day L3 Global 0.05Deg CMG MYD10C2
https://nsidc.org/data/MYD10C2/versions/61

MODIS Terra Snow Cover Monthly L3 Global 0.05Deg CMG MOD10CM
https://nsidc.org/data/MOD10CM/versions/61
MODIS Aqua Snow Cover Monthly L3 Global 0.05Deg CMG MYD10CM
https://nsidc.org/data/MYD10CM/versions/61

Data format for all products is HDF-EOS2