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Geog319RmSns > Water > Flashcards

Water Flashcards

1
Q

The interaction of EMR and water has lots in common with the interaction between EMR and what?

A

Atmosphere and vegetation

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2
Q

Attenuation =

A

Absorption and Scattering

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3
Q

What is the Lt (Total radiance) recorded by a RS system over water a function of?

A

Electromagnetic energy received from:

  • Lp, atm path radiance
  • Ls, free-surface layer (glint)
  • Lv, Subsurface volumetric reflectance, water column (water constituents)
  • Lb, Bottom reflectance (substrate, bathymetry)
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4
Q

Which spectrum penetrates the deepest in water?

A

Blue

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5
Q

Why does IR have a low reflectance for water?

A

Much of the IR is absorbed by water

- Assume it is like glint and use it to calibrate Ls (specular reflection)

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6
Q

Ls

A
  • Radiance that reaches the air-water interface (free-surface layer or boundary layer)
  • glint
  • Waves make glint on one side
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7
Q

Glint

A
  • Specular reflection on the surface of the water

- Waves can make glint on one side and increase all wavelengths radiance proportionally/equally

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8
Q

Lv

A
  • Radiance that penetrates the air-water interface
  • Interacts with organic/inorganic constituents
  • Exits water before reaching bottom
  • Subsurface Volumetric Radiance
  • Provides information about the internal bulk characteristics of water column
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9
Q

What is the main Radiance variable that influences the water colour?

A
  • Lv

- Function of water optical constituents and light

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10
Q

What are the water constituents that affect attenuation (absorption and scattering of light) for Case 2 waters?

A
  • Water
  • Colour Dissolved Organic Matter (CDOM)
  • Phytoplankton (case 1 waters)
  • Detritus and other organic material
  • Inorganic material
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11
Q

Case 2 waters

A
  • Coastal and inland
  • Complex
  • CDOM, Inorg seds, Phyto etc.
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12
Q

Case 1 waters

A
  • Oceanic
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13
Q

Why does pure water appear blue?

A
  • Blue spectrum exhibits low absorption
  • UV and Yellow through IR heavily absorbed (<400nm and >580nm)
  • IR has negligible scattering
  • Some scattering at dark-blue spectrum is slightly more than absorption
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14
Q

Which Landsat bands would be better for displaying/delineating water bodies?

A
  • Not visible, water can get lost in other information

- Use Infrared and Red, water will appear very dark due to high IR absorption and no real reflectance

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15
Q

CDOM stands for?

A

Colour Dissolved Organic Matter

  • Dissolved component leftover after plant/animal break down
  • Strong light absorber
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16
Q

Sources of CDOM

A
  • Phytoplankton w/in photic depth of water column convert consumed nutrients into organic matter using photosynthesis (primary production), then bacterioplankton decompose this organic matter
  • Humic substances from decomp of terrestrial organic matter
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17
Q

Primary production

A
  • Phytoplankton photosynthesis of nutrients converting to organic matter
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18
Q

What does decomposition of organic matter in water lead to?

A

Leads to Dissolved Organic Matter (DOM) in oceanic, near-shore and inland water bodies

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19
Q

Sunlight penetrates the water column to what depth?

A
  • Photic depth
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20
Q

If there is sufficient DOM in water, what may happen to penetration of light?

A
  • Light penetration will reduce in depth
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21
Q

How does CDOM impact water?

A
  • Impacts absorption of light in water column
  • Changes water colour
  • Can block light penetration and compete with creatures that require that light for primary production (eelgrass, phytoplankton etc.)
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22
Q

Absorption is the opposite of what?

A
  • Reflectance, assuming transmission is low
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23
Q

What colour does water with significant CDOM appear? Why?

A
  • Reddish Brown
  • High CDOM = black tea coloured water
  • CDOM heavily absorbs Low wavelengths (blue) and decreases abs towards red
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24
Q

How is CDOM measured?f

A
  • Filter out particulates, 0.2micrometer filter
  • Measure absorption of filtrate w/ spectrophotometer
  • Absorption at 440nm is proxy for CDOM concern (m^-1)
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25
Q

Why is a(440) used to approximate aCDOM?

A
  • Because CDOM will heavily absorb in this wavelength
  • Low CDOM = low a440
  • High CDOM = high a440
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26
Q

Inorganic Suspended Material

A
  • Minerals found in suspension are common
  • Size range varies from clay, silt, to fine and course sands
  • Variety of sources
  • Concentrated near inland and nearshore waters
  • Rare in deep offshore oceans (less than 1 micrometer in diameter, smaller than clay)
27
Q

What are some potential sources of inorganic suspended particles?

A

Agriculture, erosion, weathering, shore erosion (waves/boat traffic), volcanic ash

28
Q

What happens to reflectance vs. wavelength as concentration of Inorganics increases?

A
  • Scatter’s in all wavelengths, independent of nm, but generally more in short wavelengths
  • Higher inorganic conc’n = higher scatter, independent of wavelength
29
Q

How is TSS measured?

A
  • Filter water
  • Measure conc’n of material left on filter by weighing
  • Weight 1 = x (clean filter)
  • Weight 2 = x plus y (filter after 1L water, then dried, then weighed)
  • Conc’n in mg/L
30
Q

Compare measurement of CDOM vs. TSS

A
  • CDOM uses dissolved filtrate and absorption as proxy for conc’n
  • TSS uses particulate weight per L of water to get conc’n
31
Q

Why does really pristine water look purple?

A
  • Short wavelengths reflected, rest absorbed, scatters purple light at short wavelengths and Blue through Green a bit
32
Q

Clay vs. Silt size reflectance

A
  • Clay scatters more in red spectrum and reflects more IR than clear water
  • Silt scatters more in red and green, and IR over clear water
  • Increase conc’n of particles and all wavelengths will increase regardless of size but some scatter/reflect more than others
  • Size of particle determines if spectrum will be reddish or green
33
Q

Why does glacial outwash/lakes appear turquoise?

A
  • Silt size particles in water
34
Q

What is the correlation between conc’n of TSS vs. Reflectance

A
  • Highly correlated

- As TSS increases, Reflectance increases

35
Q

Secci Disk

A
  • Measures turbidity/visibility in water
  • Black and white quadrants
  • Lower into water and when it is no longer visible that is the depth that light can no longer penetrate
36
Q

Amazon River, water turbidity overview

A
  • 1 river w/ heavy mining increases sediments, discharges into Amazon
  • Amazon appears brown
  • Measure and track conc’n of seds through system using Red reflectance
  • Use Landsat time series to track change
37
Q

Amazon River, water turbidity implications

A
  • Less light for primary production = less phytoplankton = less fish
  • Changes ecosystem
38
Q

What did tracking the change of sediment conc’n in Amazon reveal over time?

A
  • Landsat time series revealed correlation of sed conc’n with price of gold
  • Gold increases, mining increases, sediment input increases
39
Q

How is sediment in river (Amazon example) measured remotely?

A
  • Using classification of remote image
  • Find areas of increased sediment input
  • Use optical index (B3-B2) x 100
40
Q

Fraser Plume, impacts

A
  • Visible = Milky whitish from seds
  • Photic zone depth is shallower
  • Scatters photosynthetically active so less is available to creatures
  • Salish Sea is more productive on periphery of plume
41
Q

Plankton

A
  • Term describes all living organisms present in water-body that cannot resist the current
  • Plants and animals
42
Q

What do all phytoplankton in water contain?

A
  • Photosynthetically active chlorophyll a pigment

- Also some chl b

43
Q

What are 2 other phytoplankton photo-synthesizing agents besides chl-a

A
  • Carotenoids, beta-carotene

- Biliproteins (phycocyanin, phycoerythrin)

44
Q

Why are phytoplankton important?

A
  • Productivity b/c base of food chain
  • Carbon Sink
  • Use to infer primary productivity in waters
45
Q

What is a reasonable surrogate for phytoplankton productivity?

A

Chlorophyl a

46
Q

Dominant chl a wavelengths of absorption

A

435 and 670-680nm

47
Q

What is red tide caused by?

A
  • Red or brown phytoplankton Dinoflagellates in the water
  • Reflects red from phycoerythrin pigment absorbing more in B and G
  • Kills shellfish and causes illness
48
Q

What does the reflectance of algae-laden water look like? What happens when suspended sediment is added?

A
  • Algae absorbs strongly in blue and red, reflects green
  • Add sediment and shift reflectance from Green to Red
  • Seds can distort reflectance of phytoplankton and affect productivity analysis, open ocean is better w/o coastal influence
49
Q

What colour is water when algae is dominant factor?

A
  • Green water because of chlorophyl
50
Q

Fluorescence

A
  • Phytoplankton can emit/reflect right before IR spectrum

- Peak can be used to evaluate phytoplankton when sediments distort reflectance but may be less accurate measurement

51
Q

What satellite platform is designed to monitor productivity?

A
  • MODIS-Aqua
  • Measures chlorophyl with bands designed for B, G, R and Fluorescence
  • Help monitor salmon in SoG and if they are getting what they need
52
Q

What is one method to aid in modelling chlorophyl in the Salish Sea?

A
  • Sensor’s on ferry measuring chl-a
  • Compare w/ satellite and find algorithm is pretty good for measuring chl-a
  • But ferry only measures on routes and satellite can measure large areas
53
Q

Lb

A
  • Radiance that reaches the bottom of waterbody, if it can get that far
  • Reflects from bottom, propagates through water column, exits column
  • Radiance is value of the bottom (depth, substrate type, algae)
54
Q

Can IR be used for Lb?

A
  • No b/c is heavily absorbed by water molecules
55
Q

In what order does light stop penetrating the water, when clear?

A

IR, R, O, UV, Y, G, V, B

- Blue penetrate deepest, usually

56
Q

What is the usual affect of light in clear water? What happens when CDOM is involved?

A
  • IR and R stop penetrating the deeper it goes and blue goes deepest
  • When CDOM involved it is difficult for light to penetrate and B and G is now absorbing, R may go further than B
  • No light left to reflect after water abs IR and R, and CDOM abs B and G
57
Q

Which SPOT band would be best for substate mapping? Why not other bands?

A
  • Band 1, Green b/c interacts w/ corals
  • Can’t use Band 3 b/c IR abs by water
  • Band 2 Red only shows some info
  • Blue Band would only be useful if no CDOM absorbing B
58
Q

Irradiance vs. Depth: Clear water

A
  • Deepest light penetration in clear water
  • B and G deepest, scattered, use to detect substrate
  • R absorbed by water molecules, doesn’t go as far
59
Q

Irradiance vs. Depth: Chl-a

A
  • G penetrates furthest, then Red, then Blue b/c of chl-a absorbance
  • Max depth btwn 9 -10m
60
Q

Irradiance vs. Depth: CDOM

A
  • R penetrates furthest b/c B and G heavily absorbed by CDOM
  • Max R penetration 5cm, B max at 10cm, G at 20cm
  • Tea-coloured almost black water colour
61
Q

Irradiance vs. Depth: Chl-a and some CDOM

A
  • B doesn’t penetrate far
  • G and R penetrate a few meters
  • G lowers w/ addition of CDOM b/c it absorbs some green, but mostly blue
62
Q

Where is CDOM usually highest?

A
  • Inland waters

- Red gives most penetration

63
Q

How to separate intertidal using Landsat TM5

A
  • Use mix of Visible and IR
  • Use IR band 5 and Visible bands 1 and 2
  • Mix b/c IR good for land and doesn’t show much water, can use this to separate the land from intertidal in B and G

Geog319RmSns (15 decks)

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