Remote Sensing Flashcards
(41 cards)
what is spatial data?
data with a known location on earth
what is GIS?
Geographic information systems
- automated systems for capturing, storage , display, manipulation and analysis of data with a know position
what are the different types of spatial data?
> 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
what is georeferencing?
> the process of assigning position (coordinates) to geographic objects on, above or below the earth’s surface
what do you need to know when using spatial data? (GPS coordinates)
> 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)
what do geographical coordinates do?
> 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
what are the two forms of output coordinate systems?
geographical coordinates and Easting and Northing Coordinates
What are easting and northing coordinates?
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
what are the components of GPS?
> 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
how do you transform images into maps?
> 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
what is elewhat is electromagnetic magnetic radiation?
> 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
what are the types of interactions recorded by remote sensing?
1) reflection/scattering
2) absorption
3) transmission
4) Fluorescence
what are some of the differences between active and passive remote sensing?
passive remote sensing cannot look through clouds, whereas active can
> there is also refraction occurring that can obscure data
what are the effect of water types on marine remote sensing?
> organic and inorganic material influencing light environment due to scattering and absorption
what is the effect of water depth on marine remote sensing?
> same feature at different water depths change colour
what is water clarity in the coastal environment?
> 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)
sensor characterisitics
> 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)
what are the sensor characteristics - scale:
> 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)
what are some sensor characteristics of spatial data?
> pixel size > extent > revisited time > spectral properties > availability > dollars
what are spectral signatures?
> 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
why are mangrove maps not easy to produce?
> due to their dense understory and geographical location
what does remote sensing provide mangroves?
> 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
what can remote sensing provide?
> 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
what are the characteristics for identifying mangrves using remote sensing data?
> 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
