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Earth from Space > Unit 7 > Flashcards

Unit 7 Flashcards

1
Q

define orbital period

A

time taken to complete one single orbit

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2
Q

the path on Earth traced by the satellite based on the orbit and FOV

A

ground track

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3
Q

define swath

A

the width of the ground area covered, based on the field of view of the sensor

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4
Q

the dimensions of the ground area covered by the scene captured by the sensor

A

foot print

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5
Q

define repeat cycle

A

time interval after which a satellite repeats its path

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6
Q

what does altitude affect?

A

the height of the platform affects spatial resolution

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7
Q

what satellite remote sensors have an equatorial crossing time?

A

polar orbiting or sun synchronous like LANDSAT

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8
Q

what inclination is polar/near polar?

A

near 90 degrees

WHICH IS RARE

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9
Q

what kind of orbit has a near 0 degree inclination?

A

equatorial

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10
Q

What is the limitation of an equatorial inclination?

A

creates a gap in data since the Northern regions of the globe won’t be seen

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11
Q

Orbit less than 90 degrees

A

PROgrade orbit (moves in direction of Earth’s rotation)

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12
Q

Retrograde orbit (moves against the direction of Earth’s rotation)

A

Inclination more than 90 degrees

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13
Q

What orbit is in sync with Earth’s spin and has a high orbit?

A

Geosynchronous (same location in the sky = always the same view)

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14
Q

What orbit crosses latitudes at the same time of day?

A

Sun-synchronous

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15
Q

What kind of inclination are sun-synchronous orbits?

A

Polar but retrograde (~98)

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16
Q

what is the consequence of a sun-synchronous orbit?

A

Either the descending or ascending node is illuminated

ex. Landsat, the descending from N-S is illuminated

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17
Q

what is the advantage of a slightly retrograde orbit?

A

Since the Earth is not a perfect sphere, each orbit is a slightly different view until eventually the entire surface is covered = Nodal Displacement

18
Q

What are the general steps of data processing?

A
  1. geo-registration
  2. calibration
  3. cloud masking
  4. atm correction
  5. index calculation
  6. analysis and interpretation
19
Q

What can be used for a reference in atmospheric reflectance statistical models?

A

Dark object subtraction: use very dark strongly absorbing features like clear water bodies as a reference (zero reflectance)

20
Q

What are radiative transfer models?

A

a physically-based model to estimate the atm scattering contribution to the signal received at the sensor

21
Q

What is the benefit of a radiative transfer model and how does it work?

A

They have less assumptions and therefore are more precise

Use ancillary data + top of atm reflectance to estimate the surface reflectance by inverting the model

22
Q

How can clouds be identified in spaceborne imaging?

A

Since they don’t emit thermal energy compared to Earth’s surface and reflect very strongly in the visible EM spectrum: you identify them by comparing thermal and visible reflectance

23
Q

How can spectral indices be used?

A

You can combine known spectral signatures to highlight certain objects using spectral bands

24
Q

What is an example of a spectral index use?

A

Normalized Difference vegetation Index (NDVI)

25
Q

What is the NDVI?

A

the comparison of reflectance in the NIR and Red band of the EM spectrum: tells us how much healthy vegetation is present

26
Q

Which sensor is a single channel detector sensitive to radiation within a broad wavelength range?

A

Panchromatic imaging systems ex. Landsat 8 pan band

27
Q

What is a multispectral imaging system?

A

A sensor with a multichannel detector with a few spectral bands; the channel is sensitive to EM within a narrow wavelength band ex. Landsat, Sentinel-2

28
Q

How many channels does a super spectral imaging system have and what are some examples?

A

MODIS, MERIS, Sentinel-3

Usually has >10, therefore narrower bandwidths with a finer spectral characteristic

29
Q

What is the benefit of a hyperspectral imaging system?

A

Increases the spectral resolution which enables better characterization and identification of targets

30
Q

How does the spectral and spatial resolution compare between Landsat and MODIS

A

MODIS has a greater spectral resolution than Landsat but a smaller spatial resolution (500m vs 30m)

31
Q

How many bands does MODIS have? Which of these bands have different spatial res and why?

A

36, 2 in 250 and 5 in 500

Need higher spatial resolution for NIR and R to calculate NIDV

32
Q

what is temporal compositing?

A

taking multiple images over a range of time to give a median, max, and average pixel reflectance since clouds make daily imaging impossible

33
Q

How is MERIS different than MODIS?

A

While it is a superspectral: there are extra bands in the visible range for chemical reactions
=harmful algal blooms monitoring

34
Q

What band is chlorophyll-A strongly absorbed

A

Red bands

35
Q

What is the purpose of Sentinel-3

A

To provide daily coverage of the globe for coastal and water quality monitoring

36
Q

How does Landsat manage data amount?

A

By off-loading to ground receiving stations using EM radiation

37
Q

What is unique about Sentinel-2?

A

4 bands in VIS + NIR at 10m resolution
6 bands in red edge + NIR + SWIR at 20m
*important for looking at crops, harvest, and drought

38
Q

What are some examples of missions that aren’t global?

A

CBERS (China + Brazil), IRS (Indian), NIGERIASAT

39
Q

Why was NIGERIASAT launched?

A

Mainly for disaster monitoring

40
Q

Who distributes Very High Resolution (VHR) Sensor imagery?

A

Usually is commercial with customers in government and private industry

41
Q

Is some VHR data public?

A

Yes under agreements for international disasters

42
Q

What are examples of VHR data?

A

Worldview, IKONOS and GEOEYE, RAPIDEYE, and SPOT

Earth from Space (9 decks)

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