Use of MODIS False Color to Monitor Snowfall, Snow melt and Thermal

BeltsGina Loss – Service Hydrologist

Dave Bernhardt – Science & Operations Officer

Great Falls, Montana

Why MODIS to monitor snow and river ice?Montana is rural with a low population densityRemote sensing best to appropriately

determine the transition of snow cover and river ice in remote areas,Problem - Visible imagery does not clearly

differentiate snow from clouds.MODIS false color composite does differentiate

snow from cloudsResult is improved assessments of flooding

potential with rapid melt and runoff

MODIS False Color CompositeComposites one visible and two infrared

channels Highlights features with infrared signature

differencesSnow and clouds have reflective differences

above 1.4μmEspecially near the 1.6μm and 2.13μm MODIS

channelsCompositing a visible channel with these two

infrared channels creates an image that distinguishes snow and clouds

Comparison to Other Satellites 

MODIS

AVHRR GOES

Spatial Resolution (meters) 500 1000 1000

Channels used to produce snow products

7 3 1 broadband

Images per day 1-2 3-6 20

Comparison to Other SatellitesMontana at a relatively high latitude and at

edges of both GOES East and WestRemapping of data results in a north-south and

east-west blurring of detailsGOES imagery can be looped to show

stationary snow features vs. moving cloudsStill issues with semi-stationary clouds

Fog Lenticular formations Orographically induced stratus

Assessment Samples

SnowCloud

sBare

Ground

Cirrus

Snow inForest

Clouds Snow

SnowCloud

sBare

Ground

Cirrus

Snow inForest

Clouds Snow

SnowCloud

sBare

Ground

Cirrus

Snow inForest

Clouds Snow

Visible Image Natural Color Image

False Color Image

River Ice Monitoring Samples

Bow-tieEffect Lake

Ice

Valley Fog

River Ice

Snow

Snow

Snow in Forests

Snow in Forests

River andLake Ice

RottingLake Ice

Bare Ground

Clouds

Snow in Forests

Snow in Forests

Rotting River andLake Ice Clouds

February 21, 2008 April 12, 2008

2004 Case AssessmentFebruary 19, 2004

Missouri

River

Milk River

Poplar River

2004 Case Assessment March 4, 2004

Missouri

River

Milk RiverPoplar River

2004 Case AssessmentMarch 11, 2004

Missouri

River

Milk River

Poplar River

2004 Case AssessmentMarch 18, 2004

Missouri

River

Milk River

Poplar River

2004 Case AssessmentMarch 25, 2004

Missouri

River

Milk River

Poplar River

Assessment of Flooding Potential

Co-op Observations

NOHRSC Model Snow DepthMonitor change

in snow cover and snow water

equivalent

Monitor change in

stream flow

NOHRSC Aerial Survey NOHRSC Flight

Lines

Satellite Imagery

NOHRSC Modeled Snow Melt

Satellite Imagery

Benefitsprovided by

MODISFalse Color

Imagery

Snow event

Inform emergency

management

NOHRSC Model Snow Water

Equivalent

USGS Streamflow

NWS Streamflow and Forecast

Facilitates monitoring 2-D change of snow cover

Illustrates stream

flow/snowmelt relationship

Faster and more

convenient

Corroborates NOHRSC snow

model products

Saves human resources and

increases safety

Provides easily

understood briefing tool

Examine snow cover

Request survey

of remote areas

SNOTEL Reports

Examine NOHRSC products

Findings - AdvantagesComplete overview of snow cover extent

High spatial and spectral resolution Information for areas void of surface data Indicates primary areas of concern when complemented with

supplemental data from ground measurements Often eliminates need for field surveys during potentially dangerous

situationsObservation of snow cover transition

Speed and extent of snowmelt provide insight to areas with possible flooding concerns 

View of ice on rivers and lakes Ice formation and degradation provide insight on locations of possible

ice jams and related floodingCorroborates information provided by NOHRSC (National

Operational Hydrologic Remote Sensing Center) snow models 

Findings – DisadvantagesCloud cover blocks view of surface

Visible and infrared spectrumsSignificant snowfall/snowmelt can occur under cloud

cover and full extent may not be viewable for daysImages per day limited

Polar-orbiting satellite provides only a few images daily

‘Bow-tie’ effect blurs imagesSatellite field of view overlap produces data

repetition at image edgeAlgorithm to remove this effect will be available soon

Fire ThreatsFires always a concern

to NWS forecastersNumerous specialized

forecasts provided for data sparse locations to support wildfire suppressionNeed all possible

observations – including satellite

Topography Western Montana

Bitte

rroo

t Val

ley

Bitte

rroo

t Mou

ntai

ns

Sapp

hire

Mou

ntai

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MODIS 3.7 micron 0930 UTC 30Aug2007

Warm Mountain

Cool Valley

Even Warmer Slopes

04 Jul 2007 Felix wildfire near the top of Bridger Range, northeast of Bozeman, MT

MODIS IR and AWIPS Topography

Felix Wildfire

Pronounced thermal belt west slopes

MODIS Derived hot spots depicted in google earth