Remote Sensing I:Basics
Kelly M. Brunt
Earth System Science Interdisciplinary Center, University of Maryland
Cryospheric Science Laboratory, NASA Goddard Space Flight Center
(Based on Nick Barrand’s UAF Summer School in Glaciology 2014 lecture)
Electromagnetic Radiation Electromagnetic SpectrumNASA Satellites and the Electromagnetic SpectrumPassive & Active instrumentsTypes of Survey MethodsTypes of OrbitsResolutionPlatforms & Sensors
(Speaker’s bias: NASA, lidar, and Antarctica…)
ROUGH Outline:
Electromagnetic Radiation
Wikipedia
- Energy derived from oscillating magnetic and electrostatic fields
- Properties include wavelength (, in m) and frequency (, in Hz) related to (speed of light, 299,792,458 m/s) by:
Electromagnetic Radiation
NASA
Electromagnetic Spectrum
(increasing frequency…)
Electromagnetic Radiation
Electromagnetic Spectrum
NASA
(increasing wavelength…)
Radiation in the Atmosphere NASA
Specular: Smooth surface; energy reflected in 1 direction (e.g., sea ice lead)
Diffuse: Rough surface; energy reflected in many directions (e.g., pressure ridges)
Nick Barrand, UAF Summer School in Glaciology, 2014
Cryosphere
NASA Earth-orbiting Satellites (‘observatory’ or ‘bus’)
NASA
Satellite, observatory, or bus: everything (i.e., instrument, thrust, power, and navigation components…) e.g., TerraInstrument: the part making the measurement; often satellites have suites of instruments e.g., ASTER, MODIS (on satellite Terra)
NASARadio & Optical; tropical rainfall
Radio; wind speed over oceans
Decommissioned
Radio; sea surface height
Optical;Earth observing
Radio & Optical; water cycle
Optical; Earth observing
Decommissioned
Radio & Optical; Ozone and air
Optical; atmosphere CO2 Radio; atmosphere CO2
Optical; aerosols
Radio; clouds
Radio & Optical+; incoming solar radiation
GRACE-FO: Gravity
Radio & Optical; climate cycle
Radio & Optical; weather
Radio; precipitation Optical; clouds
Radio; clouds
NASA Earth-orbiting Satellites (‘observatory’ or ‘bus’)
NASA Earth-orbiting Satellites (‘observatory’ or ‘bus’)
Passive & Active Sensors
Passive: reflected solar radiation (e.g., photography, visible and infrared)Passive: radiation emitted by an object (e.g., thermal infrared, passive microwave)Active: provides its own energy source (e.g., lidar, radar)
Nick Barrand, UAF Summer School in Glaciology, 2014
Snow, Ice, & Reflectance
Gardner & Sharp, 2010
Types of Sensor Arrays
Whisk broom (e.g., Landsat 7)across- and along-track scanners (sweeps)lots of coverage
Conically scanning (e.g., ATM; ACATS; vs CATS; airborne)
Push broom (e.g., Landsat 8, ASTER, SPOT)along-track scannerlots of coverage
Repeat track (e.g., ICESat, ICESat-2)static beam arrangementdiscrete sampling;interpolate between data
Harris Geospatial
Harris Geospatial
NASA
Satellite Orbits
- Polar orbit: Satellite ground track comes close to north and south poles e.g., ICESat-2
- Geostationary orbit: Satellite is in high-Earth orbit and matches Earth’s rotation e.g., GOES
- Sun synchronous orbit: Satellite in near polar orbit, maintaining same relationship to the Sun e.g., Landsat-8 A-Train: A series of NASA satellites in Sun synchronous orbit, passing over the equator at 13:30 each day e.g., Aqua, Aura
- Orbit inclination: a measure of the tilt of the satellite relative to the Earth Prograde: orbital movement is in the same direction as Earth’s rotation (inclination < 90) e.g., geostationary Retrograde: orbital movement is in the opposite direction as Earth’s rotation (inclination > 90) e.g., ICESat-2, sun-synchronous orbits
- Ascending orbit: Satellite is moving south to north (this side of the figure)- Descending orbit: Satellite is moving north to south (backside of the figure)
NASA
8298
Satellite Orbits
ISS: 400 kmICESat-2: <500 kmICESat: 500 km
AQUA/TERRA: 700 kmLandsat-8: 700 kmIridium: 700 km (constellation)
GPS: 20,000 km (constellation)
GOES (geosynchronous): 36,000 km
NASA
Sun: 150 million kmDSCOVR/EPIC: L1 (1.5 million km)
James Webb: L2 (1.5 million km)
Nope!
NASA
Satellite Orbits:ICESat-2 and repeat-track vs off-pointing
One day of ICESat-2 orbitsInclination: 92 (Polar orbit; retrograde)LEO, 500 km1387 unique tracksEvenly spaced15 per day; 91-day repeat cycle
‘Repeat-track’ mode at Poles;‘Off-nadir pointing’ mode over landCyan and red dots (left): off-nadir pointing transitions
NASA
Satellite Orbits:Space Junk
Low Earth orbit
Geostationary orbit NASA
Density at Poles
Satellite Orbits:NASA’s A-Train
NASA
Afternoon Constellation: A series of NASA satellites in Sun synchronous orbit, passing over the equator at 13:30 each day
Inclinations of ~98 (latitude limit of ~82)
Decommissioned
Exited A-train orbit
ResolutionNot to be mistaken for a measure of accuracy and/or precision
- Spatial resolution: minimum separation at which objects appear independent and isolated Dependent on altitude Generally more appropriate for raster data; i.e., pixel size EPIC/DISCOVR: 12 km WorldView-2: 0.5 m
- Temporal resolution: measure of observation frequency Dependent on FOV (MODIS: daily) Some missions have ‘seasonal’ components (ICESat-2: 91-day repeat)
- Spectral resolution: number of sensors and bands of instrument ’Hyperspectral’ ’Multispectral’…
- Radiometric resolution: how finely system can represent or distinguish differences in intensity Measure of sensitivity, or range of values coded Early sensors: 128 values (7 bits) MODIS: 4096 (12 bits)
Spatial, Temporal, and Spectral Resolution of Selected Optical Platforms
Landsat 8 2013 15, 30, 60m 16 days PAN, 6 MS, 2 TIRWorldView-4 2016 0.31m 4.5 days PAN, VIS+NIR
Nick Barrand, UAF Summer School in Glaciology, 2014
Thermal IRMultispectral
Platforms & Instruments (bias toward Crysopheric sciences)
1) Aerial photographye.g.: U-2/ER-2 airborne datae.g.: CORONA (1959!! Available 1995): Look this up!! https://en.wikipedia.org/wiki/Corona_(satellite)visible, near-infraredpassive
2) Visible and near-infrarede.g.: Landsat; MODIS; ASTER (Terra); SPOTe.g.: DigitalGlobe satellites(QuickBird, GeoEye-1, IKONOS, WorldView-1, WV2, WV3, WV4)could include stereo (SPOT, WV)passive
3) Thermal infrarede.g.: Landsat (5 – Present); MODIS; ASTERpassive
4) Laser ranginge.g.: ICESat; ICESat-2lidars for atmospheric scienceactive(More in RS3 lecture)
** 1 through 4 are limited by cloud-cover
NASA
Airbus Defense and Space
Platforms & Instruments (bias toward Crysopheric sciences)
AVISO
5) Radar altimetrye.g.: Jason-2; Jason-3; ESA radar altimetersTOPEX, Jason-1, -2, -3: 66 inclinationtimeseries of MSS changeactivecan transmit and receive through clouds
6) Passive microwavee.g.: SSM/I (DMSP satellites, 1987 - ); AMSR/E (Aqua, 2002 - 2015)passivecan detect through clouds
7) Imaging radar/Synthetic aperture radar (SAR)COSMO-Skymed (2007); Radarsat-2 (2007); TerraSAR-X (2007);TanDEM-X (2010); CryoSat-2 (2010);ALOS-2 PALSAR (2014); Sentinel-1A (2014)activecan transmit and receive through clouds
(More later from Mark)
SUMMARY
Electromagnetic radiation and Spectrum
Earth sensing satellites are generally in the Radio and Optical windows
Satellites can be described by: Passive/Active Polar, geostationary, or Sun synchronous orbit Prograde or retrograde orbit
Satellites with cryospheric applications date to 1959 (Corona)!!!
https://science.nasa.gov/ems/