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MARS2001 Module 4
Module 4
| Question | Answer |
|---|---|
| Geographic Information Systems (GIS) | automated systems for capturing, storage, display, manipulation and analysis of data with a known position |
| Raster data | spatial variables represented in a grid cell based/image format (e.g. simpler data structure) |
| Vector data | feature boundaries converted to polygons approximating original regions (e.g. lower data volume and greater spatial resolution) |
| What is georeferencing? | the process of assigning position (coordinates) to geographic above or below the earth's surface |
| What do you need to know when using spatial data (GPS coordinates) | projection (equations to convert from 3D earth to 2D map); datum (origin point for coordinates); coordinate system (location reference system, e.g. x. y) |
| What are geographical coordinates? | in form of longitude and latitude; define 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 |
| What are Easting and Northing coordinates? | equivalent to (x, y) positions; used in more localised prohjections for specific parts of the earth |
| Effect of water surface (refraction) in marine remote sensing | path of electro magnetic radiation (e.g. visible light) is refracted (changing direction) when travelling from one medium (e.g. air) to another medium (e.g. water) |
| Absorption and scattering in water | organic & inorganic material influence light environment; the same thing at different water depth changes colour due to refraction and absorption; currents, tides and wind move water causing differences in how earth observations sensors capture it |
| Rule for passive (optical) sensors: | 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) |
| How is remotely sensed data differentiated (e.g. between types of sensors)? | based on how they measure electromagnetic radiance, which is determined by spatial, spectral, temporal, and radiometric data |
| What is spatial data in remote sensing? | size of sampling unit (pixel and reoslution); extent of area covered |
| What is spectral data in remote sensing? | type of electromagnetic radiation (EMR) measured (e.g. visible light vs. thermal infrared) |
| What is temporal data in remote sensing? | time and frequency of image acquisitions; revisit time (hours, days, weeks) |
| What is radiometric data in remote sensing? | signal to noise ratio |
| Passive sensors | capture for each pixel electromagnetic radiation at specific sensitive bands, each band is a layer that is part of an image stack |
| What colours penetrate further in the water column? | blue penetrates deeper than red or near infra red bands; blue has more scattering of light as it is a lower wavelength, therefore we see more blue |
| Spectral signatures in water | spectral signatures of submerged features are limited to the visible wavelengths due to their ability to penetrate water; the signatures of different features start to look the same as you get deeper (due to absorption and scattering) |
| What are the three water types? | blue water (low sediments + phytoplankton); green water (phytoplankton rich); brown water (sediments rich); blue water reflects the most blue light back and brown water has little to no blue light reflected |
| Spectral differentiation | the number of bands, width and location of bands all help to see what you can differentiate from the bottom of the water column; different plant material has different pigments which changes the signature |
| What is a passive (optical or thermal) imagine system? | relies on reflected sunlight or emitted thermal energy; unable to use through clouds, smoke or at night; vegetation response controlled by pigments, canopy structure and biomass |
| What is an active (microwave or radar) imagine system? | relies on a transmitter/sensor configuration; able to see through clouds, smoke and at night; vegetation response controlled by water content, canopy structure and biomass; other active systems include sonar and LiDAR |
| What are the correction steps in image pre-processing? | radiometric correction; atmospheric correction; georeferencing correction; water surface (sun glint); air water interface (refraction); water column (water depth, chlorophyll, sediments); masking (e.g. land, clouds) |
| What is a pixel based mapping approach? | look to the spectral signatures from specific features (e.g. seagrass) and check every pixel in the image; if they have a similar spectral signature to set pigments |
| What is an object-based mapping approach? | look at groups of pixels; characterises by colour, texture, location, biology as a group (label segments like this) |
| What do you need to map coral reefs? | need to understand what coral habitats require (e.g. light, temp., water chemistry, depth, slope, waves and consolidation) |
| How to create maps of coral reefs? | need detailed field data, geomorphic observations and satellite images |
| Considerations when making global habitat maps | repeatable and consistent approach applicable for every reef; semi-automated by using publicly accessible methods and globally covering satellite image data sets |
| Constraints when making global habitat maps | depth; limited class differentiation (pigment concentration may be similar to hard to differentiate depending on device (spectral bands)); spatial (consistent at large scale but challenging on small scale); temporal (maps are static, monitoring dynamic) |
| What do you need to map an environment? | you need a classification scheme, a trade off between what can be measured and what is needed |
| What else can you use to differentiate mapping categories? | physical attributes (depth, slope, waves, consolidation); spatial relationship (neighbouring, enclosing, shape) |
| Reef mapping | a basis for accessing changes and trends at various scales; used for accessing effective conservation and marine protected area design, connectivity, water quality etc. |
| Sea surface temperature (SST) | measured at a depth of a meter or more by a contract thermometer (bulk thermometer); source of teh SST signal is the skin layer of the ocean, which is generally cooler than the subsurface layer because of heat flow from the ocean to the atmosphere |
| Ocean colour determination | inverse methods are applied to images to estimate their constituents and biophysical properties; more chlorophyll absorbs more light; hotter water usually attracts more plant material |
| What are biophysical properties? | pigments, organic matter, non-organic matter, suspendedm matter, dissolved matter |
| Pigments (ocean colour) | more pigments, more absorption; colour of ocean is constantly changing; different chlorophyll's have different specific light absorbing properties over specific wavelengths (by knowing these wavelengths we can predict specific chlorophyll types) |
| Suspended matter particles (ocean colour) | are sensitive at a specific wavelength (like chlorophyll); there is high suspended matter along the coastline and low levels off shore; when water is clear, easier to take measurements from satellite images (can only measure surface, not water column) |
| Water depth | different wavelength of light will penetrate water at different depths; depends on water column constitutions; need to see the bottom for satellite imagery to work for depth; depth water used for mapping how water flows (connectivity of reefs), navigation |
| SONAR meaning | sound navigation and ranging |
| LiDAR meaning | Light detection and ranging; red terrestrial, green marine |
| Coral reef watch | use products of satellite imagery to determine where hotspots are and where anomalies in SST are; aim to monitor and manage coral bleaching events and use variety of remote sensing data |
| Data used to model bleaching hotspots | Coral Watch from space; hotspot mapping (wind, temp., clarity); satellite measure SST; anomalies between observsed and seasonal SST; degree heating weeks (DHW), weeks area is hoter than normal |
| Allen coral atlas | also looks at coral bleaching; compare areas where temperature is normal vs. not normal; when SST is high, they lok at images collected during that period and create another image (only in areas we expect coral so need habitat map) |
| What is a repeatable mapping approach applied to? | various biophysical properties, short time frame (days), large areas |
Created by:
tkeen40
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