LANDSAT… the grand-daddy of satellite sensing systems

LANDSAT… the grand-daddy of satellite sensing systems

Earth Resource Technology Satellite (EARTS)

• EARTS 1 launched in 1972• Name Changed in 1975 to Landsat 1 and

Landsat 2 launched• Longest continuous remote sensing record for

the globe• Initial sensor package

– RBV (return beam vidicon) cameras projected to be the primary sensor (TV cameras)

– Multi-Spectral Scanner (MSS) a secondary sensor.

1972 2000

Land Cover/Land Use change

Las Vegas Nevada

Sun-Synchronous Orbits

• The orbital angle and speed are calculated to bring the satellite over a given latitude at a specific time.

• e.g. equatorial crossing at ~ 0945.

• Orbit advances daily … repeat coverage of a given location every 16-18 days.

Data transmission

• Image files are very large. A serious problem is onboard storage/transmission of data.

• Downlink sites receive direct transmission of data when the satellite is overhead.

• EROS Data Center (EDC) note downlink dish.

TDRSS (Tracking and Data Relay Satellite System)

• Geosynchronous data relay satellites.

• Acts as a relay device for other satellites…. Constant contact with ground station, stores and relays data from other satellites.

RBV (Return Beam Vidicon) Cameras

• Expected to be the primary sensor for Landsat

• green, red and NIR sensitive TV cameras….

• Never worked properly• Abandoned as useful data collection tools

early on• The Multi-Spectral Scanner (MSS)

became the primary sensor.

MSS data collectionRotating scan mirror focused track lines on a detector array.

Note the width of the scan track

Less than 12 degrees of angular field of view from orbit results in 185 km of image track.

Bands were originally numbered 4-7

(RBV sensors band designation 1,2,3)

Russian Far East

Landsat MSS

Band 5 (red)

1975

Scene ~185 km X 185 km

Pixel resolution ~ 80 meters

Russian Far EastLandsat MSS Band 7 (near infra-red)1975

Sovetskaya-Gavan

Airfields as references:

1.

2.

3.

1975

1989

Note change in forest area.

Deforestation….

1975

1989

Changes in technology:

• When Landsat 4 and 5 were launched, MSS is no longer the primary sensor… the primary data collection now done by the Thematic Mapper (TM)

• TM data have higher spatial (30 meter) and spectral (7 band) resolution

The TM sensor

Politics, Economics, and Data Storage in the real world.

• While the cost in designing, building and deploying a satellite is very large… the most significant cost is transmission/correction and archiving the data!

• Archiving data lacks the ‘glamour’ of a launch… it’s the boring day to day rectification and storage of information….very little money gets spent on this task.

Losing data…

• Huge quantities of Landsat 1 and 2 data are in imminent danger of being lost.

• Magnetic tapes are not stable media – The magnetic signal ‘bleeds through’ the layers of

tape– Tapes must be ‘fluffed’ on a regular basis to prevent

contamination between tape layers– The plastic of the tape also becomes brittle– 3 semi-trailer loads of tapes were found (literally)

moldering in a damp basement in Baltimore… stored in trailers at EDC waiting for $.

Politics and Economics

• What is the legitimate role of Government?

• roads? bridges? defense? social security? welfare? topographic maps? remote sensing data?

• “We hold these truths to be self-evident, that all men are created

equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. --That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed,”

Who should make decisions? Individuals (free enterprise) or government?

• In the 1980’s major effort to reduce the size and scope of government (at least on paper)

• The difficult issues never get tackled… it’s the easy targets.

• Satellite data made for an easy target• EOSAT a private corp. formed to make a profit

by selling Landsat data.• TM scenes $4,000/each!• By legislative fiat meteorological satellites kept

under government control (AVHRR data became the sensor of choice when possible)

The final Landsat…

(number 6 never made it to orbit!)

Cost structure defined by law, as cost of reproduction… limited to $600/scene

Oops! Landsat 7 has a malfunction… the “Scan Line Corrector (SLC), which compensates for the forward motion of the satellite. Subsequent efforts to recover the SLC were not successful, and the problem appears to be permanent”

The center of an SLC-off data product should be very similar in quality to previous Landsat 7 data. However, the scene edge will contain alternating scan lines of missing data

The proposed solution, fill in new scenes with interpolated data.

Data Processing levels…

• Level 0 (Raw data)

• Only useful if you're studying the RS system itself, or data processing systems

Level 1 and Level 2 processing

• Processing includes: • Radiometric correction - compensating

for known characterisitcs of the sensor. • Atmospheric correction - compensating

for the distortion (lens effect) of the atmosphere.

• Geometric correction - referencing the image to Lat/Long on the Earth's surface

Level 3 processing

• Geocoded Projected Imagery• The image is mapped to a projection

of the Earth• additional processing such as

multiple image composites, indices or ratios are created etc.

Browse Images

• “Images you can download from the net are likely to be browse images. These are typically GIF or JPEG format, although a number of others exist. Whilst providing a good idea of what is in an image, they are not useful for serious applications. They have the advantage of being a manageable size - typically of the order of 100Kb-1Mb (compared to 100Mb for a full scene) and are often available free.”