Unit 7 Flashcards
define orbital period
time taken to complete one single orbit
the path on Earth traced by the satellite based on the orbit and FOV
ground track
define swath
the width of the ground area covered, based on the field of view of the sensor
the dimensions of the ground area covered by the scene captured by the sensor
foot print
define repeat cycle
time interval after which a satellite repeats its path
what does altitude affect?
the height of the platform affects spatial resolution
what satellite remote sensors have an equatorial crossing time?
polar orbiting or sun synchronous like LANDSAT
what inclination is polar/near polar?
near 90 degrees
WHICH IS RARE
what kind of orbit has a near 0 degree inclination?
equatorial
What is the limitation of an equatorial inclination?
creates a gap in data since the Northern regions of the globe won’t be seen
Orbit less than 90 degrees
PROgrade orbit (moves in direction of Earth’s rotation)
Retrograde orbit (moves against the direction of Earth’s rotation)
Inclination more than 90 degrees
What orbit is in sync with Earth’s spin and has a high orbit?
Geosynchronous (same location in the sky = always the same view)
What orbit crosses latitudes at the same time of day?
Sun-synchronous
What kind of inclination are sun-synchronous orbits?
Polar but retrograde (~98)
what is the consequence of a sun-synchronous orbit?
Either the descending or ascending node is illuminated
ex. Landsat, the descending from N-S is illuminated
what is the advantage of a slightly retrograde orbit?
Since the Earth is not a perfect sphere, each orbit is a slightly different view until eventually the entire surface is covered = Nodal Displacement
What are the general steps of data processing?
- geo-registration
- calibration
- cloud masking
- atm correction
- index calculation
- analysis and interpretation
What can be used for a reference in atmospheric reflectance statistical models?
Dark object subtraction: use very dark strongly absorbing features like clear water bodies as a reference (zero reflectance)
What are radiative transfer models?
a physically-based model to estimate the atm scattering contribution to the signal received at the sensor
What is the benefit of a radiative transfer model and how does it work?
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
How can clouds be identified in spaceborne imaging?
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
How can spectral indices be used?
You can combine known spectral signatures to highlight certain objects using spectral bands
What is an example of a spectral index use?
Normalized Difference vegetation Index (NDVI)
What is the NDVI?
the comparison of reflectance in the NIR and Red band of the EM spectrum: tells us how much healthy vegetation is present
Which sensor is a single channel detector sensitive to radiation within a broad wavelength range?
Panchromatic imaging systems ex. Landsat 8 pan band
What is a multispectral imaging system?
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
How many channels does a super spectral imaging system have and what are some examples?
MODIS, MERIS, Sentinel-3
Usually has >10, therefore narrower bandwidths with a finer spectral characteristic
What is the benefit of a hyperspectral imaging system?
Increases the spectral resolution which enables better characterization and identification of targets
How does the spectral and spatial resolution compare between Landsat and MODIS
MODIS has a greater spectral resolution than Landsat but a smaller spatial resolution (500m vs 30m)
How many bands does MODIS have? Which of these bands have different spatial res and why?
36, 2 in 250 and 5 in 500
Need higher spatial resolution for NIR and R to calculate NIDV
what is temporal compositing?
taking multiple images over a range of time to give a median, max, and average pixel reflectance since clouds make daily imaging impossible
How is MERIS different than MODIS?
While it is a superspectral: there are extra bands in the visible range for chemical reactions
=harmful algal blooms monitoring
What band is chlorophyll-A strongly absorbed
Red bands
What is the purpose of Sentinel-3
To provide daily coverage of the globe for coastal and water quality monitoring
How does Landsat manage data amount?
By off-loading to ground receiving stations using EM radiation
What is unique about Sentinel-2?
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
What are some examples of missions that aren’t global?
CBERS (China + Brazil), IRS (Indian), NIGERIASAT
Why was NIGERIASAT launched?
Mainly for disaster monitoring
Who distributes Very High Resolution (VHR) Sensor imagery?
Usually is commercial with customers in government and private industry
Is some VHR data public?
Yes under agreements for international disasters
What are examples of VHR data?
Worldview, IKONOS and GEOEYE, RAPIDEYE, and SPOT
