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MARS2014 > Remote Sensing > Flashcards

Remote Sensing Flashcards

1
Q

what is spatial data?

A

data with a known location on earth

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2
Q

what is GIS?

A

Geographic information systems

- automated systems for capturing, storage , display, manipulation and analysis of data with a know position

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3
Q

what are the different types of spatial data?

A

> raster
- spatial variables represented in a grid cell based/image format
- more calculations
vector
- feature boundaries converted to polygons approximating original regions (e.g., lower data volume and greater spatial resolution
- digitised
- faster

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4
Q

what is georeferencing?

A

> the process of assigning position (coordinates) to geographic objects on, above or below the earth’s surface

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5
Q

what do you need to know when using spatial data? (GPS coordinates)

A

> projection - equations to convert from 3-D earth to 2-D map
Datum - origin point for coordinates
coordinate system - location reference system (x,y,latitude, longitude, easting, northing)

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6
Q

what do geographical coordinates do?

A

> in the form of longitude and latitude, uniquely define the location of any point on the surface on Earth with no need for mapping zones and without any distortion, since it is based on angles
most common in marine environment

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7
Q

what are the two forms of output coordinate systems?

A

geographical coordinates and Easting and Northing Coordinates

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8
Q

What are easting and northing coordinates?

A

are equivalent to (x,y) positions and are used in more localised projections for specific parts of the earth, such as transverse mercator, which produced map zones that are 6 degrees of longitude wide

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9
Q

what are the components of GPS?

A 
> there are 24 satellites
> 6 orbital planes
> 20,000km high
> 12 hour orbits
> any weather
> challenges under trees or high buildings
> at least 4 satellites in view 24 hours per day
> GPS does not work underwater
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10
Q

how do you transform images into maps?

A

> each image pixel contains a measure of reflected sunlight in selected sections of bands (e.g., Blue, Green, Red, Near Infra Red)
sunlight is a form of electromagnetic magnetic radiation
image processing algorithms are applied to each image pixel to identify “what” is in it or to estimate the “biophysical value” (e.g., water depth)
satellite layers sensitive to different light

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11
Q

what is elewhat is electromagnetic magnetic radiation?

A

> sunlight is a form of EMR
thermal energy (heat) is a form of EMR
any material with molecular motion (T>0K) emits radiant energy with energy level dependent on temperature
EMR = ultra-violet, visible (blue-green-red), infrared, thermal infrared, microwave/radio waves

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12
Q

what are the types of interactions recorded by remote sensing?

A

1) reflection/scattering
2) absorption
3) transmission
4) Fluorescence

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13
Q

what are some of the differences between active and passive remote sensing?

A

passive remote sensing cannot look through clouds, whereas active can
> there is also refraction occurring that can obscure data

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14
Q

what are the effect of water types on marine remote sensing?

A

> organic and inorganic material influencing light environment due to scattering and absorption

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15
Q

what is the effect of water depth on marine remote sensing?

A

> same feature at different water depths change colour

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16
Q

what is water clarity in the coastal environment?

A

> clear - you can (almost) always see the bottom, even in deeper water
clear to turbid - you can see the bottom through most of the area
turbid - you can (almost) never see the bottom, even in knee deep water
A general rule for passive sensors (optical sensors) is:
- if the bottom is visible you can map the substrate or features on it (optically shallow water)
- if the bottom is not visible you cannot map the substrate or features on it (optically deep water)

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17
Q

sensor characterisitics

A

> satellite movement:
- sun-synchronous polar orbit (e.g., they always capture at day light) and cover the earth surface (600-800 km orbit)

> Geostationary Earth orbit, follow same spot on earth (35000km orbit)

18
Q

what are the sensor characteristics - scale:

A

> remotely sensed data are differentiated based on how they measure Electro Magnetic Radiance, which is determined by:
spatial
- size of sampling unit (pixel and resolution)
- extent of area covered
spectral
- type of Electro magnetic Radiation EMR (light) measured e.g., visible light versus thermal infrared
- how sensitive (wavelengths)
temporal
- time and frequency of image acquisition
- revisit time (hours, days, weeks)

19
Q

what are some sensor characteristics of spatial data?

A 
> pixel size
> extent
> revisited time
> spectral properties
> availability
> dollars
20
Q

what are spectral signatures?

A

> they describe the amount of light reflected by a feature measured at different wavelengths
spectral signatures of features submerged in water are limited to the visible wavelengths due to their ability to penetrate water.
the highest values are associated with the brightest items

21
Q

why are mangrove maps not easy to produce?

A

> due to their dense understory and geographical location

22
Q

what does remote sensing provide mangroves?

A

> provides indirect access to mangrove forest
enables extrapolation of observation results at sampling site to entire image
ability to deliver data at multi-scale levels
multi-temporal ability

23
Q

what can remote sensing provide?

A 
> habitat inventories
 - determination of extent, species and composition
 - health status
> change detection and monitoring
 - land use
 - land cover
 - conservation and reforestation success
 - silviculture
 - aquaculture and development
> ecosystem evaluation support
> productivity assessment
 - biomass and carbon estimation
> regeneration capacity estimation
> multiple management requests
 - fisheries
 - aquaculture activities
 - conservation management
 - management guidelines and strategies
> field survey planning
> water quality assessment
> prompt information supply for disaster management
> aid delivery to gain a better understanding of ecological and biological relations and processes, functions, and dynamics
24
Q

what are the characteristics for identifying mangrves using remote sensing data?

A

> topographical setting
- low land area in the land-sea interface
mangrove zonation
- sequential change of bands of vegetation or tree species parallel to shore
textual characteristics
- spatial homogeneity/heterogeneity
object based approach
- colouring different objects; saltmarsh, mangrove etc
- mangrove species

25
Q

what causes variation in mangrove zonation?

A

> due to rising level of the land and the frequency of tidal inundation, soil salinity, water table depth, waterlogging, soil drainage, soil type and freshwater inflow
this can be varied across different sites

26
Q

what are the methods for mapping turbid to clear water?

A

> turbid
- manual delineation: field data + depth contours + expert knowledge.
clear to turbid
- as above
- pixel based classification: Landsat imagery (30m pixel, 4 bands + field data)
NOTE: field data is always required for mapping and validation

27
Q

what are the steps for creating seagrass maps?

A

1) high spatial resolution imagery
2) radiometric, atmospheric and geometric correction
3) corrected high spatial resolution imagery
> produces maps of seagrass % cover, species, biomass, all on a fine scale

28
Q

how do you correct high spatial resolution imagery?

A

> photo transect surveys
photo analysis
species and cover class per point

29
Q

what is special about a biomass map?

A

> biomass is 3D

> so from a core sample you need the species, horizontal % cover, and weight

30
Q

what is the spatial scale of a reef system?

A

> 20km

> covers a series of reefs

31
Q

what is the spatial and information scale of reef types?

A

> 2km

>fringing, lagoon or barrier

32
Q

what is the spatial and information scale of geomorphic zones?

A

> 500m

> slope, crest, lagoon

33
Q

what is the spatial and information scale of benthic community?

A

> 1m
sand, rubble algae
algae, coral, sand
coral rock

34
Q

what is the spatial and information scale of biotech/patch

A 
>0.25m
> coral
>algae
> benthic micro algae
> sand
> rubble
> rock
35
Q

how do you assign labels to different pixels?

A

> assign labels to segments based on eco-geomorphological relations between mapping features at all spatial scales

36
Q

what do large reefs have variation in?

A

> 300km^2

  • reef composition (e.g. coral, seagrass, algae)
  • depth
  • number and type of imagery to cover full extent
  • date/time of image capture, causing variations in:
  • tidal range
  • water clarity
  • water roughness
  • atmospheric conditions
37
Q

how is object based image classification superior in large reefs?

A

> better deal with variation as it takes not only colour into account of groups pixels, but also texture and eco-geomorphological characteristics

38
Q

what is the toss up with accuracy of object based image classification?

A

> the higher the number of mapping categories, the less accurate the map

39
Q

how do you map geomorphic zonation and benthic cover?

A

> geomorphic zonation:
- mapped using satellite image based mapping techniques
Benthic cover type:
- mapped by combining established satellite-mapping and empirical modelling approaches

40
Q

how does wave type effect the composition of coral reefs?

A

> you can predict the type of coral community based on information of waves and coral cover
need the wave climate of the reef
need the geomorphic map
need the benthic map
empirical model to predict coral type on reef slope based on field data, water depth, geomorphic maps and wave exposure models

41
Q

give a summary of coral reef mapping

A

> mapping approach based on high spatial resolution multi-spectral imagery, field data and object based image classification.
repeatable mapping approach, applied to:
- different reefs
- small and large reefs
- time series
a basis for accessing changes and trends at various scales: reef, geomorphic, benthic community and patch
solomon’s and fiji maps are used for accessing effective conservation and marine projected area design

MARS2014 (3 decks)

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