1. SnowEx: a NASA airborne campaign leading to a snow satellite mission
SnowEx Organizing Committee: Edward Kim, Charles Gatebe, Dorothy Hall, Matthew Sturm, Noah Molotch, Chris Crawford, DK Kang, Eugenia De Marco, with contributions by many others
NASA Headquarters Program Manager: Jared Entin
June 14, 2016
Snow Watch
Columbus, Ohio

2. Outline Background Sites Instruments & Aircraft
Satellite Mission Concept
Summary
For more information, see
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3. What is SnowEx?
A multi-year airborne snow campaign designed to collect multi-sensor aircraft data and ground truth measurements to enable algorithm development and design a future satellite mission
SnowEx is all about challenging the sensing techniques and algorithms…. to learn when, where and how each technique works alone, or in synergy with other techniques, and why
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4. SnowEx Driving Questions
What is the optimum combination of sensing techniques to measure
regional (global) SWE?
global snow melt/energy balance (where, when, how fast)?
The SnowEx experiment design must be developed in the context of a future spaceborne measurement system
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5. When is SnowEx? Year 1 = 2016/17 fall and winter: campaigns
Year 2 = 2017/18 winter: no campaign
Year 3 = 2018/19 winter : campaign
Year 4 = 2019/20 winter : campaign
Year 5 = 2020/21 winter : campaign
“Campaign” includes (ideally)
Fall -- no-snow background observations with lidar and radar
Winter -- dry snow observations with full sensor suite
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6. Where will SnowEx take place?
In Year 1 the experiment will take place in Western Colorado
Grand Mesa – meets all four Year 1 requirements
Uncompaghre/Senator Beck – good but lacks adequate flat terrain to be the main site
Site selection was primarily based on the requirements needed to achieve SnowEx objectives
See snow.nasa.gov for a comparison of sites, and for further details on potential sites
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7. Site Requirements (1) Probability of wet snow is very low
(2) Existence of a shallow to deep gradient in snow depths and SWE
(3) Snow-covered area with flat terrain that is larger than airborne instrument swath widths
(4) Forested stands with variable density and height
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8. Forest-Cover Gradient
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9. Advantages/Strengths Remote Sensing techniques for global snow
Radar (SAR): senses SWE and melt, high resolution through clouds and darkness
Passive MW: senses SWE and melt through clouds and darkness (very long record from satellite data)
Lidar: snow depth, accuracy acceptable for deeper snow, SWE (need density), very high resolution, possibly through forest gaps
Multispectral: MODIS/VIIRS, fSCA, albedo, grain size, IR, moderate spatial resolution
Hyperspectral: fSCA, albedo, surface grain size, moderate/high spatial resolution
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10. Instruments
From the 2016 Seattle iSWGR / SnowEx workshop, the core sensor types for Year 1 are:
Lidar
Radar (SAR)
Passive microwave
Passive VIS/IR
Radiometer for sensing BRDF
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11. JPL’s Airborne Snow Observatory (ASO) has been selected by HQ for Year 1
ASO uses a Riegl Q1560 scanning lidar, which captures the surface topography with <10 cm vertical accuracy. Depth is calculated by subtracting a summer “snow-free” dataset from each winter “snow-on” dataset. The accuracy of these data is dependent upon precise knowledge of the aircraft position during the measurements. An integrated Applanix Inertial Measurement Unit (IMU) and GPS provide aircraft attitude and position information, and this information is combined with error corrections from an existing network of GPS base stations at fixed locations near the survey area. This combined use of the IMU for high-speed attitude information, along with the differential GPS solution for absolute position, yields the sub-decimeter aircraft trajectory accuracy necessary for LiDAR snow depth measurements.
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12. ESA’s SnowSAR
Twin frequency [9.6 and 17.2 GHz (X- and Ku- bands)] polarimetric Synthetic Aperture Radar
High frequencies will allow the study of both the surface and underlying layers of the snowpack because they have different backscattering properties
ESA commissioned MetaSensing, a company based in Noordwijk, The Netherlands, to develop and test the SnowSAR instrument
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13. The Airborne Earth Science Microwave Imaging Radiometer (AESMIR)
The AESMIR is a passive microwave airborne imager with 6 microwave bands (6, 10, 18, 23, 36, 89 GHz) with 4-Stokes polarization capability (except at 23 GHz)
18 & 36 GHz, V &H pols are useful for snow; 10 & 89 GHz are of secondary interest for snow
Programmable scan modes include conical and cross-track scanning
Requires heavy-lift aircraft such as a P-3 aircraft
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14. Passive VIS/IR Cloud Absorption Radiometer (CAR) More info at
BRDF capability
Multi-spectral: 14 bands (0.34 to 2.29 µm)
Mature
More info at
Publication:
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15. Snow mission concepts Must address global snow
Therefore must include multiple sensors (community consensus)
Active & passive mw, lidar, multi-spectral VIS/IR
Need mature technology and algorithms
SCLP and CoReH2O both suffered on radar algorithms
Satellite mission must avoid high cost
Leverage existing assets (satellite PM and multispectral)
But some satellite assets might go away (PM?)
International partnering is the key to
Leveraging technology and algorithm development investments
Spreading costs
Some sensors can/should be suborbital
E.g., Lidar on aircraft and other sensors on satellites
Societal benefits and science return already strong
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16. Summary
SnowEx: a NASA airborne campaign leading to a snow satellite mission
Instrument payload designed to determine what combination of sensors provides the optimum results for measuring SWE, BRDF, surface temperature and mass
SnowEx Year 1, , will be held in Western Colorado – fall and winter campaigns
Out years ( , and ) will likely take place in other locations
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