Remote Sensing I: Basics
Kelly M. Brunt
Earth System Science Interdisciplinary Center, University of Maryland Cryospheric Science Laboratory, NASA Goddard Space Flight Center kelly.m.brunt@nasa.gov
(Based on Nick Barrand’s UAF Summer School in Glaciology 2014 lecture) ROUGH Outline:
Electromagnetic Radiation Electromagnetic Spectrum NASA Satellites and the Electromagnetic Spectrum Passive & Active instruments Types of Survey Methods Types of Orbits Resolution Platforms & Sensors
(Speaker’s bias: NASA, lidar, and Antarctica…) Electromagnetic Radiation
- 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:
Wikipedia Electromagnetic Radiation
Electromagnetic Spectrum
NASA
(increasing frequency…) Electromagnetic Radiation
Electromagnetic Spectrum
NASA
(increasing wavelength…) Radiation in the Atmosphere NASA
Cryosphere
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 NASA Earth-orbiting Satellites (‘observatory’ or ‘bus’)
NASA Satellite, observatory, or bus: everything (i.e., instrument, thrust, power, and navigation components…) e.g., Terra Instrument: the part making the measurement; often satellites have suites of instruments e.g., ASTER, MODIS (on satellite Terra) NASA Earth-orbiting Satellites (‘observatory’ or ‘bus’)
Radio & Optical; weather Optical; atmosphere CO2 Radio; clouds Radio; atmosphere CO2 Radio; clouds Radio; precipitation Optical; clouds Optical; aerosols
Optical; Earth observing
Radio & Optical; Ozone and air
Decommissioned
Radio & Optical; water cycle
Radio & Optical; climate cycle
Optical; Decommissioned Earth observing
Radio; sea surface height GRACE-FO: Gravity Radio & Optical; tropical rainfall NASA
Radio & Optical+; incoming solar radiation Radio; wind speed over oceans 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) Harris Geospatial
Push broom (e.g., Landsat 8, ASTER, SPOT) along-track scanner lots of coverage
Harris Geospatial Repeat track (e.g., ICESat, ICESat-2) static beam arrangement discrete sampling; interpolate between data
NASA 82 Satellite Orbits 98
NASA
- 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) Sun: 150 million km Satellite Orbits DSCOVR/EPIC: L1 (1.5 million km)
James Webb: L2 (1.5 million km)
NASA
ISS: 400 km ICESat-2: <500 km Nope! ICESat: 500 km
AQUA/TERRA: 700 km Landsat-8: 700 km Iridium: 700 km (constellation)
GPS: 20,000 km (constellation)
GOES (geosynchronous): 36,000 km
NASA Satellite Orbits: ICESat-2 and repeat-track vs off-pointing
One day of ICESat-2 orbits Inclination: 92 (Polar orbit; retrograde) LEO, 500 km 1387 unique tracks Evenly spaced 15 per day; 91-day repeat cycle
‘Repeat-track’ mode at Poles; ‘Off-nadir pointing’ mode over land Cyan and red dots (left): off-nadir pointing transitions NASA Density at Poles Satellite Orbits: Space Junk
Low Earth orbit
NASA Geostationary orbit Satellite Orbits: NASA’s A-Train
Afternoon Constellation: A series of NASA satellites in Sun synchronous orbit, passing over the equator at 13:30 each day
Exited A-train orbit
Decommissioned
Inclinations of ~98 (latitude limit of ~82) NASA Resolution Not 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
Nick Barrand, UAF Summer School in Glaciology, 2014
Landsat 8 2013 15, 30, 60m 16 days PAN, 6 MS, 2 TIR WorldView-4 2016 0.31m 4.5 days PAN, VIS+NIR Platforms & Instruments (bias toward Crysopheric sciences)
1) Aerial photography e.g.: U-2/ER-2 airborne data e.g.: CORONA (1959!! Available 1995): Look this up!! https://en.wikipedia.org/wiki/Corona_(satellite) visible, near-infrared passive
2) Visible and near-infrared e.g.: Landsat; MODIS; ASTER (Terra); SPOT e.g.: DigitalGlobe satellites (QuickBird, GeoEye-1, IKONOS, WorldView-1, WV2, WV3, WV4) could include stereo (SPOT, WV) passive
3) Thermal infrared Airbus Defense and Space e.g.: Landsat (5 – Present); MODIS; ASTER passive
4) Laser ranging NASA e.g.: ICESat; ICESat-2 lidars for atmospheric science active (More in RS3 lecture)
** 1 through 4 are limited by cloud-cover
Multispectral Thermal IR Platforms & Instruments (bias toward Crysopheric sciences)
5) Radar altimetry e.g.: Jason-2; Jason-3; ESA radar altimeters TOPEX, Jason-1, -2, -3: 66 inclination timeseries of MSS change active can transmit and receive through clouds
6) Passive microwave e.g.: SSM/I (DMSP satellites, 1987 - ); AMSR/E (Aqua, 2002 - 2015) passive can detect through clouds
7) Imaging radar/Synthetic aperture radar (SAR) COSMO-Skymed (2007); Radarsat-2 (2007); TerraSAR-X (2007); AVISO TanDEM-X (2010); CryoSat-2 (2010); ALOS-2 PALSAR (2014); Sentinel-1A (2014) active can 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/ [email protected]