Lecture 6 remote sensing systems Flashcards
Describe Landsat
World’s longest continuously acquired collection of space-based land remote sensing data
▪ Data consistent since 1972
▪ Visits the same place every 16 days (temporal resolution = 16 days)
▪ 30-meter spatial resolution (visible & shortwave IR) each pixel is 30x30, each has 7 spectral wavebands
▪ Data publicly available at no cost, designed to monitor environmental change such as deforestation
- Can easily compare across time
How does Landsat acquire data
▪ Satellite in a polar-orbit with an altitude of 705km
▪ Swath of 185km – width, satellite scans left to right
▪ 16-day repeat cycle with an equatorial crossing time of 10:00 a.m (temporal resolution) – can be an issue with clouds – particularly in the tropics.
▪ >700 images daily in the Worldwide Reference System-2 (WRS-2) path/row system
Moderate resolution of 30x30m but at the time this would have been considered high
What are the landsat sensors (RBV) (MSS) (TM) (ETM+) OLI (1 & 2) TIRS (1 & 2)
Landsat 1,2,3. Return Beam Vidicon (RBV) camera/Multi Spectral Scanner (MSS)
Landsat 4,5. Multi Spectral Scanner (MSS) / Thematic Mapper (TM)
7 Enhanced Thematic Mapper+ (ETM+)
8.9 Operational Land Imager – OLI (1 & 2), Thermal InfraRed Sensor – TIRS (1 & 2)
Why is Landsat good at comparing across different time periods.
Continuity between the sensors (which are on different satellites) which have similar spectral wavebands.
How does sentinal 2 compare to landsat
Sentinel 2 has better spatial and temporal resolution than Landsat
Describe sentinal 2
Multispectral imager (MSI).
13 bands in the visible, NIR and SWIR part of the spectrum
high spatial resolution 10m, 20m, 60m
wide field of view: 290km
revisit: 5 days (with 2 satellites) under same viewing conditions
sentinel does Contains wavebands in the ‘red-edge’ ▪ Part of the spectrum which is sensitive to the vegetation chlorophyll content ▪ 680 – 730 nm
relationship between spectral measurements and chlorophyll content - can see how healthy vegetation is globally.
describe planet labs
▪ Private Earth imaging company founded in 2010
▪ Designs and develops CubeSats
▪ miniature satellites (‘Doves’) ▪ 10x10x30 centimetres ▪ Cheaper to launch
▪ 3 – 5m spatial resolution
▪ >180 satellites in orbit
▪ 4 or 8 spectral bands ▪ (blue, green, red and NIR)
▪ Image swath 32 x 20 km narrower due to its high spatial resolution.
▪ Satellites operate in constellations ▪ provide frequent global coverage ▪ higher revisit times (~30 hours – temporal resolution)
Advantages and disadvantages of planet labs
disadvantages – so many in orbit which interferes with astronomy, but benefits mean can collect frequent data.
High spatial resolution data
▪ Useful for mapping heterogeneous surfaces such as urban areas. Application - monitoring infrastructure - using it to monitor the war in Ukraine.
High spatial resolution data can aid detection of forest degradation due to selective logging ▪ Canopy closure in June masks the effects.
what are the Flagship of NASA’s Earth Observing System of satellites
▪ Terra (launched Dec, 1999) ▪ Aqua (launched May 2002)
▪ Both satellites have series of instruments to observe the total Earth system, and the effects of natural and humaninduced changes on the global environment
▪ Satellites carry a number of sensors to measure the land & ocean surface and atmospheric composition
(MODIS)
Moderate Resolution Imaging Spectroradiometer . Designed to provide global observations of the Earth’s land, oceans, and atmosphere
* Acquires data at 3 different spatial resolutions – 2 bands between .620µm and .876µm at 250 m – 5 bands between .459µm and 2.155µm at 500 m – 29 bands between .405µm and 14.385µm at 1 km
* 4 times a day (0130,1030,1330, 2230) – Important for observing diurnal cycles (e.g., temperature, anthropogenic activity) can monitor day and night.
How many wavebands does the thematic mapper have?
7 (BGR, NIR, SWIR, TIR)
What is the temporal resolution of the multispectral instrument on sentinel 2?
5 days (to get back to the same location) can monitor events that occur rapidly.
