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)

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/

kelly.m.brunt@nasa.gov