Spectral Reflectance To Elevation Data Flashcards by Bitch Rich

A portion of the incident energy that is reflected by the surface feature as a function of wavelength

Spectral Reflectance

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Spectral Reflectance Curve (Definition)

graph of spectral reflectance of a surface feature as a function of wavelength

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Spectral responses measured by remote sensors over various features often permit an assessment of the type and/or condition of the features.

Spectral Signatures

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Certain wavelengths where the curves will be absorbed and reflected

Spectral Signatures

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Measured by remote sensors may be quantitative, but they are not absolute

Spectral response patterns
(It is quantitative since spectral reflectance curve would be actual recorder values and it is distinctive for every spectral response for a certain value but it varies for different materials)

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Spectral Reflectance and spectral emitting (for wavelengths greater than 3.0 micrometer) are referred to in this manner

Spectral Signatures

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Peaks at the graph are called

Spectral pattern

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Sudden rise in peaks in the graph

Typical red edge

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Present in all healthy vegetation

Chlorophyll reflectance

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Valleys in the graph

Absorption

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Used as benchmark for vegetation stress

Red Edge

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0.8 nm to 1.4 nm (due to cell structure of vegetation)

Chlorophyll reflectance

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Factors that affects the spectral patterns

temporal effects
spatial effects

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Spectral curves that can ID materials in certain spectral regions only

Spectral response patterns

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Spectral response that allows assessment of type/conditions of features

Spectral signatures

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Changes in spectral characteristics over time.
Ex. Spectral characteristics of many vegetation are in a nearly continual state of change throughout growing season. Changes influence in the collection of data for a particular reason

Temporal effects

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Differences of the same type of features from different geographical locations

Spatial effects

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A method to measure temporal effects on features based on variations in spectral response of the feature under consideration
—– detect what has changed in a given image

Change Detection

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Any factors that change the spectral characteristics of a feature over time

Temporal effects

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What happens to the spectral patterns of plants during RAINY SEASON?

Water absorption valley will be more defined. Dominant green colors

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What happens to the spectral patterns of plants during PEAK OF SUMMER SEASON?

There are water absorption but it is not as high as rainy season. Less dominant green colors

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Spectral Reflectance difference between green grass and dry grass

*green grass - 45% SR red band
*dry grass - 65% SR red band

What we see is ratio of BGR band. Whatever you see in the Physical world is always a combination of these 3 bands.
*rainy season - higher reflected G band
*summer season - smaller ratio between BGR:GR band than it is in healthu green grass

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Refer to factors that cause the same types of features at a given point in time to have different characteristics at different geographic locations

Spatial Effects

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Banana Plantations: Benguet vs Indonesia
- same species, same farming techniques
- they differ from soil and weather
What type of spectral pattern to be considered?

Spatial Effects

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It should be noted that the apparent spectral response from surface features cab be influenced by ___?

SHADOWS

The total reflected energy is reduced, and the spectral response is shifted toward shorter wavelength.

Shadow

*ma'am showing a land cover map* Q: Where is the remote sensing here?

Every small square represents a spectra. In the original RS data each pixel is a curve. From the curve they can identify if that feature is a forest agri or built-up areas pixel based on the spectra. The image had numerous wavelengths which represents the spectral response of the ground. ----the map is just a presentation of results

Appears when the object become black or blue because of Rayleigh Scattering. Rayleigh Scattering - most of the time you will have higher energy return in the shorter wavelengths and that's the reason why the bluer side would have higher reflectance resulting to images that one slightly bluer than the other parts.

SHADOW

Radiance: "brightness" or energy received by the sensor

Atmospheric Effects on Spectral Response Patterns

2 effects of the atmosphere

1. Attenuates (reduces) energy from the sun 2. Reflects energy from the sun (path radiance

Incoming radiation

Irradiance

Incident vs extraneous radiation.

Incident radiation refers to the radiation that is emitted by the target object being observed and reaches the remote sensing instrument. Extraneous radiation, on the other hand, refers to any radiation that is not emitted by the target object but still reaches the remote sensing instrument. This can include radiation from the atmosphere, surrounding objects, or even the instrument itself.

Explain the diagram showing the Atmospheric effects influencing the measurement of reflected solar energy

The attenuated sunlight and skylight is reflected from a terrain element having reflectance. The attenuated radiance reflected from the terrain element combines with the path radiance to form the total radiance recorded by the sensor.

Effects of Path Radiance

- surface reflectance - top of atmosphere (TOA) reflectance - Atmospheric correction

The relative dominance of sunlight vs skylight in any given image is strongly dependent on_____

Weather conditions

Values with the seasonal changes in solar elevation angle and the changing distance between the earth and sun

Irradiance

Sensor positioned close to the earth's surface, the path radiance will be generally ____

small or negligible (To short for Scattering to occur)

Primarily the a function of the surface roughness of the object

Geometric Influences on spectral response patterns

- mirror-like -

Specular Reflectors

- aka Lambertian - uniform reflection in all directions - RS is more interested in this

Diffuse Reflectors

Solar elevation vs azimuth vs viewing angle (spectral response patterns)

Solar elevation angle determines the amount of solar radiation received (diurnal), solar azimuth angle determines the direction of the radiation (seasonal or latitudinal), and viewing angle determines the amount and direction of reflected energy measured by the sensor (topographic).

What is the effect of differential shading?

Differential shading is the uneven distribution of solar radiation on a target object due to variations in the angle and intensity of the Sun's rays. This can cause variations in the spectral reflectance of different parts of the target object, with areas receiving more direct solar radiation having higher reflectance and areas in shadow having lower reflectance. Differential shading can be problematic in complex topographic regions and can be corrected using algorithms that account for variations in solar elevation and azimuth angles, as well as the topographic characteristics of the target object

Mathematical solution on how reflectance varies from all combinations of illumination and viewing angles at a given wavelength

Bidirectional reflectance distribution function (BRDF)

Localized bright areas where the azimuth and xenith angles of the sensor are the same as those of the sun.

Hotspots

The existence of Hotspot is due to the fact that ____

the sunlit portion of all objects in the area, without any shadowing.

- Uses electrical signals that corresponding to energy variations in the original al scene. - Stored in a magnetic or optical computer storage medium

Digital Sensors

Images detected and recorded in film

Photographs

Pictorial records other than in film (thermal, radiation, etc.)

Images

Common exception to the rules in the terminologies used in image acquisition

Digital photography

Refers to the use of digital sensors and instruments to capture images of the Earth's surface or other objects from a distance.

Digital Imagery

- Brightness value or pixel value - average radiance in each pixel (ground sampling area)

Digital Number (DN)

Quantifying original electrical signals from sensors to positive integers

Analog-to-digital (AD) signal conversion

Three bands (wavelength) displayes in RGB

Color Composite Images

Use the natural wavelength in RGB

True color image

Other combination of bands

False color image

Each pixel includes multiple DNs, one for each spectral band

Digital Multispectral Image

Each band of data is stored as a separate file or as a separate block of data within a single file.

Band Sequential Format (BSQ)

Image data file contains first a line of data from band 1, then the same line of data from band 2, and each subsequent band.

Band Interleaved by line format (BIL)

the format contains each band's measurement for the first pixel, then each band's measurement for the pixel, and so on

Band Interleaved by pixel format (BIP)

Topographic information collected in the z axis in addition to the XY coordinates of a typical image

Elevation Data

Similar to a digital image but radiance values (DN) is replaced by elevation values

Digital Elevation Model (DEM)

Shows expected shading patterns under a set of illumination conditions

Shaded Relief

Uniform tone

Flat elev

Light facing slopes

Brighter tone

Slopes facing away from the light

Darker tone

Draped Imagery over DEM

3D perspective view

Bare/bald earth model

Digital Terrain Model (DTM)

Uppermost surface in every pixel

Digital Surface Model (DSM)

CHM

Canopy Height Model

Unprocessed elevation data representing all xyz measurements

Point cloud