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Remote Sensing of Water, Soil, and Urban Areas Lecture 6. Summer Session 28 July 2011. Spectral characteristics of water. http://www.itek.norut.no/vegetasjon/fenologi/introduction/ndvi.html. Liquid Water Absorption.

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slide4

http://www.itek.norut.no/vegetasjon/fenologi/introduction/ndvi.htmlhttp://www.itek.norut.no/vegetasjon/fenologi/introduction/ndvi.html

important things to remember in using vis rir data to monitor water surfaces
Important things to remember in using VIS/RIR data to monitor water surfaces
  • Pure water absorbs EM energy in most of the IR region
  • Pure, deep (> 50 m) water bodies have low reflectance in the visible and very near IR region of the EM spectrum
  • However, some EM energy in this region is transmitted into the water column, where it reacts with particles suspended in the water column
slide8

Variations in image color/intensity in the Bahamas region is due to reflectance off the ocean bottom

slide12

Pyrrophytes (dinoflagellates)

Oblique aerial photograph of red tide

simple model of flux off of a water surface
Simple model of flux off of a water surface

p- scattered/reflected from particles suspended in water

r- surface reflection

i

s- scattered from water

b – reflected from the bottom

what can happen to em energy reaching a water surface
What can happen to EM energy reaching a water surface?
  • Reflected off the surface
  • Transmitted into the water column
  • Absorbed by the water
  • Scattered by the water
  • Absorbed by materials suspended in the water
  • Reflected or scattered by matter suspended in the water
  • Reflected off of the bottom
water attenuation c
Water Attenuation c()

c () =  () + b ()

where

  • () = water absorption coefficient

b () = water scattering coefficient

absorption and wavelength
Absorption and wavelength
  • Note that wavelengths > 0.9 m have large absorption coefficients
  • Because of this, sea surface remote sensing systems do not have bands > 0.9 m
  • Absorption will change if you have dissolved inorganic or organic material in the water, depending upon the compounds that are dissolved
role of suspended sediments
Role of suspended sediments

Suspended sediments in the water column do two things

  • Absorb/transmit EM energy
  • Scatter/reflect EM energy
simple model of flux off of a water surface1
Simple model of flux off of a water surface

p- scattered/reflected from particles suspended in water

r- surface reflection

i

s- scattered from water

p total scattering from the water column is dependent on
p - total scattering from the water column is dependent on
  • b () - water scattering coefficient
  • SM () - Suspended inorganic minerals
  • DOM() - Dissolved organic material
  • Chl () - Chlorophyll within the column

Wavelength dependent!

t total absorption from the water column is dependent on
T - total absorption from the water column is dependent on
  •  () - water absorption coefficient
  • SM () - Suspended inorganic minerals
  • DOM () - Dissolved organic material
  • Chl () - Chlorophyll within the column

Wavelength dependent!

slide26

Chlorophytes

Euglenophytes

Haptophytes

Bacillariophytes

Glaucophytes

Pyrrophytes (dinoflagellates)

slide28

Without sediment present

Effects of phytoplankton on water surface reflectance

@ different sediment concentrations

Figure 12.9 Jensen

effects of bottom reflectance
Effects of bottom reflectance
  • In clear, shallow (< ~30 m) water, the reflectance properties of the bottom influences the total flux off of the water surface
  • Therefore, in clear shallow water, variations in total flux are related to the composition of the bottom itself
sources of variation in bottom reflectance
Sources of variation in bottom reflectance
  • Variations in mineral content of soil (sediment), gravel, rocks on bottom
  • Presence of coral
  • Presence of sea grass
simple model of flux off of a water surface2
Simple model of flux off of a water surface

r- surface reflection

i

  • Surface reflection has three components
  • Direct specular reflection of sunlight
  • Specular reflection of indirect, scattered light
  • Sunglint
slide33

Sunglint occurs when the sensor and the reflected sunlight having the same angle

  • Wind results in small waves (capillary waves) on any water surface.
  • These waves results in facets that result in direct specular reflection of a certain portion of sunlight.
  • Specular reflection off of a smooth ocean = artificially high signal at sensor.
  • Specular reflection off of a rough surface = artificially low signal at sensor.
sunglint
Sunglint
  • “Sunglint is a phenomenon that occurs when the sun reflects off the surface of the ocean at the same angle that a satellite sensor is viewing the surface.
  • “In the affected area of the image, smooth ocean water becomes a silvery mirror, while rougher surface waters appear dark.”

Source: Wikipedia – generally not to be trusted but good for sunglint!

water summary
Water Summary

In summary, total radiance from a water surface, t-wis comprised of

1. Radiance from surface reflection

2. Radiance from water scattering

3. Radiance from reflection/scattering from particles/phytoplankton suspended in the water column

4. Radiance from reflection of EM energy from the bottom of the water body

clouds
Clouds
  • Do not reflect Solar radiation well in all directions
  • Need multiple observations from different points
  • Thermal properties are important
albedo
Albedo
  • a measure of reflectivity of a surface or a body
  • a ratio of EM radiation reflected to the amount incident upon it
  • Reflectance of an object aggregated over a broader segment of the EM spectrum (0.3-2.4 microns) in all directions
  • Expressed in 0-100%
    • Clouds: varies from 10-90%, depending on drop sizes, liquid water or ice content, thickness of a cloud, and the solar zenith angle.
clouds1
Clouds

Information and imagery from http://earthobservatory.nasa.gov/Library/Clouds

high clouds
High Clouds

High clouds increase greenhouse effect and subsequently increase surface temperature

Information and imagery from http://earthobservatory.nasa.gov/Library/Clouds

middle and low clouds
Middle and Low Clouds

Low clouds decrease greenhouse effect and subsequently decrease surface temperature

Information and imagery from http://earthobservatory.nasa.gov/Library/Clouds

deep convective clouds
Deep Convective Clouds

Deep convective clouds do not influence greenhouse effect and are neutral to surface temperature

Information and imagery from http://earthobservatory.nasa.gov/Library/Clouds

precipitation
Precipitation

Hurricane Bonnie precipitation from TRMM data

snow and ice
Snow and Ice
  • Climate change observations
  • Hazards (avalanches etc.)
  • Sea ice extent
  • Fresh water supply
clouds and ice spectral response
Clouds and Ice: spectral response
  • Very similar in visible and NIR wavelengths
  • Very different in wavelengths over 1.5µm

- snow and ice strongly absorb the energy

- clouds strongly reflect the energy

Source: http://www.cps-amu.org/sf/notes/m1r-1-8.htm

soil composition
Soil composition
  • Several layers contributing to energy flux off of soils:
  • litter
  • Organic matter content
  • minerals
  • iron compounds
  • bedrock

http://cals.arizona.edu/pubs/garden/mg/soils/images/p3large.gif

http://www.physicalgeography.net/fundamentals/images/soil_breakdown.gif

energy target interactions
Energy-Target Interactions

General Rule:

I = R+A+T

Where

R – reflected radiation;

A – absorbed radiation;

T – transmitted radiation

For Soils:

I = R+A

T is near 0

general spectral characteristics
General Spectral Characteristics
  • Dry soil: increase in reflectance with increase in wavelength in visible and NIR portion of the spectrum
  • The differences in reflectance of various soils are relatively consistent throughout various wave length regions.
texture
Texture

Texture – relative proportion of clay (<0.002mm), silt (0.002 – 0.05 mm) and sand (0.05 – 2 mm) particles present in a mass of soil.

Texture

moisture content surface roughness

texture particle size
Texture: particle size

http://images.google.com/imgres?imgurl=http://dbs.umt.edu/sci226/gifs/images/lab_soils/img3_small.gif&imgrefurl=http://dbs.umt.edu/sci226/lab8_soils.htm&h=270&w=359&sz=17&tbnid=r6PqflSXM5gJ:&tbnh=87&tbnw=117&hl=en&start=3&prev=/images%3Fq%3Dsoil%2Brelative%2Bparticle%2Bsize%2Bsoil%26hl%3Den%26lr%3D%26sa%3DG

http://www.geog.plym.ac.uk/labskills/Images/triangle.gif

texture moisture content
Texture: moisture content

silt soil

sandy soil

  • Soil texture determines the ability of soil to contain large amounts of water.
  • Clay particles have strong hydroxyl absorption at 1.4 and 2.2 micrometers
  • The finer the soil texture, the greater the soil’s ability to maintain a high moisture content in the presence of precipitation.
  • The greater the soil moisture, the more incident radiant energy absorbed, the less reflected energy.

clay soil

texture moisture content1
Texture: moisture content
  • With the increase in moisture content, reflectance decreases, particularly in water-absorption bands (1.4, 1.9, 2.66, 2.73, and 6.27 micrometers)
  • The decrease in reflectance is NOT directly proportionate to the increase in moisture content
global distribution of soils water holding capacity
Global distribution of soils water holding capacity

LOW

MODERATE

HIGH

http://soils.usda.gov/use/worldsoils/mapindex/whc.jpg

organic matter
Organic matter

http://images.google.com/imgres?imgurl=http://www.na.fs.fed.us/spfo/pubs/n_resource/wetlands/images/p21pic3.jpg&imgrefurl=http://www.na.fs.fed.us/spfo/pubs/n_resource/wetlands/wetlands5_soils.htm&h=331&w=183&sz=46&tbnid=_zGkFvH9AMMJ:&tbnh=114&tbnw=63&hl=en&start=4&prev=/images%3Fq%3Dorganic%2Bsoils%26hl%3Den%26lr%3D

organic matter1
Organic matter
  • Amount of organic matter (more matter – lower reflectance)
  • Degree of decomposition
  • (more decomposed – lower reflectance)
iron oxide
Iron Oxide

http://images.google.com/imgres?imgurl=http://www.na.fs.fed.us/spfo/pubs/n_resource/wetlands/images/p21pic3.jpg&imgrefurl=http://www.na.fs.fed.us/spfo/pubs/n_resource/wetlands/wetlands5_soils.htm&h=331&w=183&sz=46&tbnid=_zGkFvH9AMMJ:&tbnh=114&tbnw=63&hl=en&start=4&prev=/images%3Fq%3Dorganic%2Bsoils%26hl%3Den%26lr%3D

iron oxide1
Iron Oxide
  • Increase in iron oxide causes decrease in reflectance in the visible spectrum but does not significantly affect wavelengths over 1.1 micrometers
texture surface roughness
Texture: surface roughness
  • IN THEORY, with a decrease in particle size, surface becomes smoother and more reflective.
    • This assumes that the soils contain no moisture, organic content, or iron oxides.
    • So, a perfectly dry, clayey soil = higher reflectance
    • But... We know clay holds water, which decreases overall reflectance, particularly in the mid-IR
  • The relationship between the amount of silt particles and surface reflectance is almost directly proportional.
soils summary
Soils Summary
  • All other things held constant...
    • Reflectance decreases with an increase in moisture content.
    • Reflectance increases with a decrease in particle size.
    • Reflectance increases with a decrease in surface roughness.
    • Reflectance decreases with an increase in organic matter content.
    • Reflectance decreases with an increase in iron dioxide content.
caveats
Caveats

Soil is a very complex mixture of materials which affect its absorptance and reflectance characteristics.

Soil characteristics are closely interrelated which significantly affects reflectance characteristics.

geomorphology applications of remote sensing
Geomorphology applications of Remote Sensing
  • Geological features and landforms
  • Coastal landforms and processes
  • Desertification
  • Glacial landforms and processes
  • Fluvial landforms and processes
  • Natural hazards
  • Soil erosion

Go through the next few slides on your own

Information and imagery from NASA Remote Sensing tutorial (section 17) http://rst.gsfc.nasa.gov

fluvial landforms 1 stream flow
Fluvial landforms (1): stream flow

Radar imagery of river network

Landsat imagery of river network in South Yemen

Meandering Mississippi

fluvial landforms 2 river deltas
Fluvial landforms (2): river deltas

Arabian sea delta

Mississippi delta

fluvial landforms 3 other
Fluvial landforms (3): other

Niagara Falls

Great Lakes

glaciers
Glaciers

Alaskan Alpine glaciers

Icecap in southern Iceland

Gulf of Alaska:

Combination of Landsat and DEM

e olian
Eolian

Refers to the activity of the winds, and their ability to shape the Earth’s surface.

coastal
Coastal

Fjords

Outer banks NC

Atoll

land cover vs land use
Land cover vs. Land use
  • Parks
  • Pasture
  • Logging concession
  • Water bodies
  • Coniferous forests
  • Deciduous forests
  • Grasslands
  • Croplands
  • Urban areas (commercial & residential)
  • Aquacultures
challenges
Challenges
  • Urban landscapes are very diverse in terms of materials present on the ground
    • This leads to mixed pixels, even at Landsat’s spatial resolution.
  • Usually has relatively small objects of interest – requires high and very high resolution
    • High = 30 meters
    • Very high = <1-10 meters
  • Urban areas have specific seasonality
    • They will look different in fall vs. winter due to vegetation change (wavelength dependent).
slide75

1 x 1 m

4 x 4 m

10 x 10 m (SPOT)

20 x 20 m (SPOT)

30 x 30 m (Landsat TM)

how to identify urban features
How to Identify Urban Features
  • Shape!
  • Texture!
  • Best detected in visible and NIR (thus cyan cities in your lab exercises)
  • Helpful information from thermal IR
slide79

1975

1995

slide80

1974

1,040 urban hectares

1994

3,263 urban hectares

315% increase