Summary
The National Park Service and the Geographic Information Network of Alaska (GINA) developed an algorithm to derive snow cover climatology for Alaska using the MODIS snow cover daily product.
The algorithm is two-fold and involves both data processing and the derivation of snow cover metrics. Terra MODIS snow cover daily 500m grid data version 5 (MOD10A1.v005) are processed to reduce cloud obscuration through iterations of cloud reduction methods that include spatial, temporal, and snow cycle filtering. A total of 12 metrics (e.g., date of first snow, date of persistent snow cover) for each pixel are calculated.
Data Sources
The MODIS Terra Snow Cover Daily L3 Global 500m Grid data (MOD10A1.v005) from the National Snow and Ice Data center (NSIDC) is used to calculate the snow metrics. Data description can be accessed at NSIDC Data Portal.
The MOD10A1.v005 data files can be downloaded from the NSIDC DATAPOOL. You must be registered as a NASA earthdata user to download data.
The MOD10A1.v005 data contains snow cover, snow albedo, fractional snow cover, and Quality Assessment (QA) data along with corresponding metadata. It consists of 1200 km by 1200 km tiles of 500 m resolution data gridded in a sinusoidal map projection. For our purposes, we downloaded 24 tile files covering the Alaska region, created a mosaic, reprojected them into the Alaska Albers Projection (NAD83), and output the four scientific fields of snow cover, snow fraction, snow quality, and snow albedo into four single band GeoTIFF files, respectively.
MOD10A1.v005 data cover the timeframe from 2000.02.24 to 2017.01.01. NSIDC released the MODIS Terra Snow Cover Daily L3 Global 500m Grid data version 6 (MOD10A1.v006) recently. The new data covers from 2000.02.24 to present. GINA and NPS have developed the MODIS_Snow_metrics_algorithm version 006 to calculate the snow metrics against MOD10A.v006. New snow metrics based on version 6 MOD10A1 will be available soon.
Product Details
The snow metrics will be updated yearly. Now 2001 to 2020 snow-year metrics are available through GINA’s ftp server. ENVI files are available as one image file and one header file. geoTIFF format is also available.
Snow-metrics data file defines the following 12 snow metrics:
- first_snow_day, first day of the full snow season (FSS start day)
- last_snow_day, last day of the full snow season (FSS end day)
- fss_range, last_snow_day-first_snow_day +1
- longest_css_first_day, first day of the longest CSS segment (CSS start day)
- longest_css_last_day, last day of the longest CSS segment (CSS end day)
- longest_css_day_range, longest_css_last_day-longest_css_first_day +1
- snow_days, the number of snow days
- no_snow_days, the number of no snow days
- css_segment_num, the number of CSS segments
- mflag, pixel type (ocean, land, or lake/inland water) and type of snow (no snow, broken snow, or continuous snow)
- cloud_days, number of cloud days
- tot_css_days, total number of all days within CSS segments
Additional Notes:
- Days reported as metrics are counted as day of year beginning on Jan.1 of the year that precedes the name of the snow year. For example, the days reported in the snow metrics of the 2010 snow year are counted from Jan.1, 2009.
- The values and their descriptions in mflag are defined in Table 1. Definition of mflag
| ocean (1) | land (2) | lake (3) | |
| no-snow (10) | 11 | 12 | 13 |
| broken-snow (20) | 21 | 22 | 23 |
| css-snow (30) | 31 | 32 | 33 |
Sample plots for snow metrics
Additional Information
National Park Service agency contact: Peter Kirchner ( peter_kirchner@nps.gov )
Snow metrics algorithm documentation is available in PDF format.
Deriving Snow Cover Metrics for Alaska from MODIS
by Chuck Lindsay, Jiang Zhu, Amy E. Miller, Peter Kirchner and Tammy L. Wilson
Remote Sens. 2015, 7(10), 12961-12985; doi:10.3390/rs71012961
Received: 27 May 2015 / Revised: 11 September 2015 / Accepted: 26 September 2015 / Published: 30 September 2015
Snow Cover Monitoring with MODIS Satellite Data in Alaska’s National Parks, 2000-2015
by Jessica E. Cherry, Jiang Zhu, and Peter B. Kirchner
Natural Resource Report NPS/SWAN/NRR – 2017/1566
Published: December 2017
Acknowledgements
Chuck Lindsay, Amy E. Miller, Parker Martyn from National Park Service Anchorage
for developing snow metrics algorithm
Michael E Budde for evaluation and feedback of snow metrics algorithm
Geographer – US Geological Survey
Earth Resources Observation and Science (EROS) Center
David K. Swanson for evaluation and feedback of snow metrics algorithm
Ecologist, Arctic Network
National Park Service