reflectance

Question 1

incident energy

Answer 1

energy from the sun that reaches the earth’s surface. It can be:
- absorbed
- reflected
- transmitted

Question 2

incident energy equation

Answer 2

incident energy (Ei) = reflected energy (Er) + absorbed energy (Ea) + transmitted energy (Et)

Question 3

what satellites measure

Answer 3

reflected energy in W/m^-2
- Er depends on the amount of incident radiation + reflection properties of surfaces
Er = Ei - (Ea + Et)

Question 4

Reflectance curve

Answer 4

X-axis: wavelength
Y-axis: reflectance
- shows what wavelengths are getting reflected back depending on the band/item

Question 5

what percent of energy is reflected by an object

Answer 5

Reflected energy / incident energy

Question 6

red edge

Answer 6

Transition of absorption between green to IR can be used to identify plants

Question 7

in plants: when moisture content is high, there’s ____ absorption

Answer 7

more
- May be helpful in measuring leaf status

Question 8

how to distinguish clouds vs snow

Answer 8

clouds: reflect high in all wavelengths
snow: reflect high in visible to near IR, absorb more in mid-IR and beyond

Question 9

what affects spec. curves in plants

Answer 9

• height of plant
• time of year
• if it’s been watered recently

Question 10

reflectance vs radiance

Answer 10

radiance: total energy measured at the satellite
- highest in blue b/c it scatters the most
reflectance: % of incident energy reflected
- because of differences in magnitude of EM radiation across wavelengths, these curves look very diff

Question 11

specular reflection

Answer 11

angle of reflection = angle of incidence
- mirror like reflections
- Usually happens equally across wavelengths
i. Doesn’t contain information about the color of what you’re looking at
1) When you’re looking at a mirror, you can’t tell what it’s made of just by looking at it; you’re only looking at your reflection

Question 12

difuse reflection

Answer 12

• reflect uniformly in all directions
• contains spectral information about the reflecting surface
  !! what we want to measure in remote sensing !!

Question 13

types of reflectors

Answer 13

• ideal specular reflector
• near perfect specular reflector
• near-perfect diffuse reflector
• ideal diffuse reflector

Question 14

ideal specular reflector

Answer 14

one to one; angle of incidence is exactly angle of reflection

Question 15

near perfect specular reflector

Answer 15

angle of incidence is angle of reflection, but some diffusion occurs

Question 16

near-perfect diffuse reflector

Answer 16

almost perfect equal reflectance in all directions, but small angle of reflection

Question 17

ideal diffuse reflector

Answer 17

perfectly equal reflection in all directions

Question 18

Something that’s more textured relative to the wavelength will cause __ reflectance

Answer 18

Something that’s more textured relative to the wavelength will cause more reflectance

Question 19

sun-sensor geometry

Answer 19

• affects reflectance measured by a remote sensing instrument
• this relative positions of the sun, sensor, and object cause geometric effects on irradiance

Question 20

sun sensor geometry: angles

Answer 20

solar elevation angle: angle between sunlight and ground
viewing angle: between camera and object
azimuth angle: ground angle between camera and sun

Question 21

differential shading

Answer 21

the sensor receives more info from one side of an object than the other bc that’s where the sun is hitting it

Question 22

differential scattering

Answer 22

a. When light is preferentially scattered in a certain direction
b. Often in mie scattering
c. Can mean light is inconsistent across angles
i. The magnitude of haze can affect the imaging

Question 23

specular reflection

Answer 23

Different distortion across different parts of the image based on the viewing angle
- i.e. a bright spot in a body of water

Question 24

bidirectional reflectance distribution function

Answer 24

mathematical function that predicts for a given object, what reflectance will be at any viewing angle and sun elevation angle
- If you’re looking at something from a particular angle and if the light source is coming from a particular angle, it predicts the reflectance
- Property of a feature
Calculated with light and viewing angle

Question 25

BRDF and spheres example

Answer 25

each sphere's BRDF describes its reflectance in terms of wavelength, illumination, and viewing angle - They look different because they're made of different things, and thus have different BRDFs ○ They reflect differently and have different wavelengths Specular and diffuse reflection also depends on the type of material

Question 26

BRDF in remote sensing: example

Answer 26

If amazonian rainforest get greener during the dry season § The first group; looked greener because they weren't correcting for the BRDF § Gave the illusion that it was greener during the dry season ○ THUS: correcting for the BRDF can affect findings § Most satellite data we collect is corrected for already

Question 27

satellites and reflectance

Answer 27

Reflectance: what a satellite is seeing - reflected light must travel twice thru the atmosphere - Some scattering happens as light returns to the sensor - Sensor picks up path radiance

Question 28

path radiance

Answer 28

scattered light that the sensor is seeing that's not reflected off of whatever the sensor is focused on

Question 29

TOA vs surface energy

Answer 29

TOA: top of atmosphere - to understand surface features, need to convert energy measured at the satellite to energy measured at the surface

Question 30

gamma and x-rays

Answer 30

almost fully blocked by the atmosphere, therefore of no use in satellite remote sensing - Cant make it thru atmosphere so not used in satellite, but used in outer space analysis

Question 31

UV wavelengths

Answer 31

0.01 - 0.4 nm - mostly blocked by the earth's atmosphere - some applications for mapping oil spills

Question 32

visible wavelengths

Answer 32

0.4-0.7 nm - atmospheric windows allow most visible light through - panchromatic imagery - measures reflectance in all visible wavelengths

Question 33

infrared

Answer 33

near IR - many applications: vegetation monitoring; delineating water bodies shortwave IR - 1.4 - 3nm - applications: soil moisture; vegetation water content; geology - can penetrate clouds

Question 34

far infrared

Answer 34

3-10,000 nm - emitted by warm objects - used to measure earth surface temperatures, detect fires

Question 35

microwave

Answer 35

- 0.1-3.0 cm - RADAR wavelengths - little solar radiation in this range, so typically requires active sensors - influenced by soil moisture, 3d structures of earth surface features - can penetrate clouds