NON-PHOTOGRAPHIC SYSTEMS: Multispectral Scanners

Medium and coarse resolution sensor comparisons:

Landsat, SPOT, AVHRR and MODIS

CLASSIFICATION OF NONPHOTOGRAPHIC REMOTE SENSORS

PASSIVE ACTIVE

SAR LASER DIGITAL CAMERA

VIDEO CAMERA

MULTI-SPECTRAL SCANNERS

MICROWAVE

THERMAL (e.g. TIMS)

VISIBLE & NIR HYPERSPECTRAL (e.g. AVIRIS)

ACROSS TRACK (sweep)

e.g. Landsat, AVHRR

ALONG TRACK (push)

e.g. SPOT

ACROSS-TRACK / MULTISPECTRAL SCANNING OPERATION

scan angle (IFOV)

pixel

scan lines

• An oscillating mirror scans across the

terrain at right angles to the flight path • mirrors direct the radiation from the IFOV to spectrum-separating devices which divide the signal into discrete bands or channels • the signal from each band is focused on detector elements that transform the radiation into an electrical signal, which is recorded and stored digitally

ALONG-TRACK SCANNING OPERATION

• linear array of CCDs “scan” perpendicular

to the flight line (no mirrors) • each CCD senses energy from a single ground resolution cell (pixel) • each spectral band (channel) requires its own CCD array • each scan line is viewed by all channel arrays simultaneously

• Advantages of along-track scanners

– linear arrays afford longer residence time for which to measure energy from each ground resolution cell, resulting in a stronger signal

– fixed relationship of CCDs along each scan line results in improved geometric integrity

– CCDs small in size and require less power for operation

– w/o moving parts (e.g. oscillating mirrors), a linear array system has a higher reliability and longer life expectancy

NON-PHOTOGRAPHIC SYSTEMS

• The Landsat Concept (emerged in late 1960s) – Launch a dedicated, unmanned land-observing satellite to

collect, archive and distribute remotely sensed data to users in agriculture, forestry, environmental science, geology, land cover/use, water resources, and marine science.

• History

– Landsat-1 launched in July, 1972

– Landsats 1 - 3 carried RBV and MSS sensor

– Landsat-4, launched 1982, carried new Thematic Mapper (TM) sensor, Landsat 5 also carries TM.

– Landsat 5 recently decommissioned (November 2012)

– Landsat 6 launch failed

– Landsat-7, with Enhanced TM sensor, launched April 1999, but developed a line scan anomaly problem that compromised the data and made it unusable for most users

– Landsat 8 Operational Land Imager (OLI) launched February 2013

LANDSAT PROGRAM (USA)

TM scene: bands 4,5,3

color composite

(Sioux Falls, SD)

• 8 bit data (0-255 DNs)

• data strips “framed” into a

185x185 km scene

• 30m ground resolution per

pixel with non-thermal

detectors

(120m for thermal band 6)

Wavelength (mm)

0.4 0.5 0.6 0.7 0.8 2.0 0.9 1.5 2.5

7 1 2 3 4 5

TM Bands:

Landsat 8 OLI bands are similar to Landsat

TM except two visible blue bands so band 1

TM is band 2 OLI, TM 3 is OLI 4, etc.

LANDSAT TM: sensor applications

TM BandWavelengthRange (mm)

Spectral Region Applications

1 0.45-0.52 Bluewater penetration, coastal mapping,soil/veg. discrimination, culturalfeature ID

2 0.42-0.60 GreenChlorophyll reflection band (peakgreen reflectance of veg.), veg. IDand vigor, cultural feature ID

3 0.63-0.69 RedChlorophyll absorption band(Vegetation discrimination),cultural feature ID

4 0.76-0.90 Near IRVeg. types, plant stress, biomasscontent, soil mositurediscrimination, water delineation

5 1.55-1.75 Mid-IRSoil and veg. moisture content,clouds vs. snow

6 10.4-12.5 Thermal IRVegetation stress, soil mositurediscrimination, thermal mapping

7 2.08- 2.35 Mid-IRVeg. moisture content, rock andmineral discrimination

OLI band

2

3

4

5

6

7

Landsat 8

Operational Land Imager (OLI)

Landsat Data

Continuity

Mission

(LDCM)

Bands Wavelength

(micrometers)

Resolution

(meters)

Band 1 - Coastal aerosol 0.43 - 0.45 30

Band 2 - Blue 0.45 - 0.51 30

Band 3 - Green 0.53 - 0.59 30

Band 4 - Red 0.64 - 0.67 30

Band 5 - Near Infrared (NIR) 0.85 - 0.88 30

Band 6 - SWIR 1 1.57 - 1.65 30

Band 7 - SWIR 2 2.11 - 2.29 30

Band 8 - Panchromatic 0.50 - 0.68 15

Band 9 - Cirrus 1.36 - 1.38 30

Band 10 - Thermal Infrared (TIRS)

1 10.60 - 11.19 100

Band 11 - Thermal Infrared (TIRS)

2 11.50 - 12.51 100 Worldwide Reference System-2 (WRS-2) path/row system

Sun-synchronous orbit at an altitude of 705 km (438 mi) 233 orbit cycle; covers the entire globe every 16 days (except for the highest polar latitudes) Inclined 98.2° (slightly retrograde) Circles the Earth every 98.9 minutes Equatorial crossing time: 10:00 a.m. +/- 15 minutes

LANDSAT TM data acquisition for Maine

• Worldwide Reference

System (WRS)- 8 scenes

• Imagery archived and

catalogued by USGS EROS

Data Center (Sioux Falls)

• Glovis Search archive on

web for available imagery

• Search parameters:

– WRS Path / Row

– date

– maximum cloud cover

– browse images

• Systeme Pour l’Observation de la Terre (SPOT)

– French Space Agency, along-track (pushbroom) scanner – SPOT-1, SPOT-2 and -3 (launched 1986, 90 and 93,

respectively): 3 spectral bands (20m ground resolution) + Panchromatic band (10m)

– SPOT-4 (1998), adds 20m Middle Infrared (MI) or Short Wave Infrared (SWIR) band

– SPOT-5 (2002), 10 m multispectral (3 bands), 20m MI or short wave, 5m panchromatic (2 sensors capable of 2.5 m panchromatic)

– Two identical High Resolution Visible (HRV) imaging systems (using CCD detector arrays): 1 Panchromatic, 1 multispectral

– pointable optics enable nadir and off-nadir scanning for greater repeat coverage and stereo viewing

– used in forestry, agriculture, ecological, land cover/use, and topographic mapping applications

SPOT Sensor System (French)

sun-synchronous orbit

altitude: 822 km

orbital period: 101 minutes (14+

orbits/day)

repeat coverage (nadir): 26 days

however off-nadir:approx. 5 days

swath: 60km at nadir, 80km on

west and east off-nadir

SPOT PROGRAM orbital and sensor characteristics

High Resolution Visual (HRV) sensor

• Advanced Very High Resolution Radiometer (AVHRR) sensor

– National Atmospheric and Oceanic Administration meteorological satellites (7 in series)

– now with 5 spectral bands: 1 visible, 1 near-IR, 3 thermal-IR

– applications: weather and climate; water surface temperature measurement; snow cover mapping; flood monitoring; global vegetation mapping and changes; regional soil moisture, fire, storm, and volcanic monitoring; mapping regional drainage and physiographic features

NOAA SATELLITES (USA)

AVHRR orbital characteristics

• Altitude: 833km

• 2400 km swath width

• 1.1 km ground resolution at nadir

• twice daily coverage

• Daylight and nighttime orbits

SENSOR COMPARISONS spectral resolution (#bands and location)

4

Thermal

Reflected

Mid_infrared

Orbit: 705 km, 10:30 a.m. descending node (Terra) or

1:30 p.m. ascending node (Aqua), sun

synchronous, near-polar, circular

Swath

Dimension

2330 km (cross track) by 10 km (along track at

nadir)

Launch

Dates

TERRA_MODIS December 1999

AQUA_ MODIS May 2002

Spatial

Resolution

250 m (bands 1-2)

500 m (bands 3-7)

1000 m (bands 8-36)

MODIS (USA)

Orbit, swath width and sensor resolution

Multi-resolution (250, 500, 1000m) and hyperspectral at 1000m resolution

MODIS (250m,500m) and Landsat TM and Reflected Bands Comparison

Band/Sensor MODIS Landsat

Red 0.620-0.670µm 0.63-0.69µm

NIR 0.841-0.876µm 0.76-0.90 µm

Blue 0.459-0.479µm 0.45-0.52 µm

Green 0.545-0.565 µm 0.52-0.60 µm

Middle-IR 1.230-1.250µm

Middle-IR 1.628-1.652µm 1.55-1.75µm

Middle-IR 2.105-2.155µm 2.08-2.35µm

Resolution 250m, 500m 30 m

Swath width 2330 km 185 km

Temporal Daily 16 days

Price Free $600/sceneFree as of

2009

Landsat 8 OLI

0.64-0.69

0.85-0.88

0.45-0.51

0.53-0.59

1.57-1.65

2.11-2.29

SENSOR COMPARISONS area covered by one scene

SENSOR COMPARISONS and Data Costs

Cost Update (4/2009)

MSS –free if available

TM/ETM+/OLI(30m) = Free

(ETM+ includes 15m Pan)

SPOT-4(MS or Pan)= $1900?

SPOT-5(10m or 5m)= $3375?

AVHRR/MODIS are

Free- Internet download

Old! Costs

Ecosystem Sensor System Spatial Extent Grain Size Plant ID Level

Biome,

continent

AVHRR,

MODIS 1000m

Hundreds of

thousands sq.

km.

1 km – 500m General land

cover (Level 1)

Regional,

country

MODIS 250m,

Landsat TM

and OLI

Thousands of

sq. km.

500- 30m General land

cover

(level 1-2)

State,

ecoregion,

watersheds

Landsat, TM

and OLI,

SPOT, others,

SAR

Hundreds of sq.

km.

30 – 10 m Forest type

(level 2-3)

Local

landscape ,

forest stands

Spot, IKONOS,

LIDAR, Digital

Cameras,

Aircraft

Hyperspectral

Tens to low

hundreds of sq.

km.

10 – 1m Forest

type/species

group and

detailed land

cover (Level 3-

4)

Forest plot Highest

resolution

sensors, ground

< ten sq. km. to

one-ten ha or

less

1m – 1 ft Tree or canopy

measurement,

some single

species ID

SENSOR COMPARISONS

• Landsat MSS – archival, historical (no longer collected), oldest earth

resource satellite at medium spatial resolution (1972) • Landsat TM, ETM+& Landsat 8 OLI

– improved multispectral resolution (7 bands (more for OLI). – Older TM historical archive than SPOT – Has visible blue & thermal band (SPOT does not) – larger area coverage and less cost (free) /area (than SPOT)

• SPOT HRV – Improved geometric quality (along track scanner, but

Landsat 8 OLI now has along track scanning) – off-nadir viewing (stereo possible) and more frequent revisit

than Landsat – Better spatial (5m -Pan and 10m Multispectral) than Landsat

• NOAA AVHRR and MODIS – Huge area covered, twice daily repeat coverage, better

temporal resolution than Landsat or SPOT – MODIS at 1000m has highest spectral resolution (36 bands) – regional applications and global vegetation monitoring – May be too coarse for many applications but free data