Spectral Reflectance To Elevation Data Flashcards
A portion of the incident energy that is reflected by the surface feature as a function of wavelength
Spectral Reflectance
Spectral Reflectance Curve (Definition)
graph of spectral reflectance of a surface feature as a function of wavelength
Spectral responses measured by remote sensors over various features often permit an assessment of the type and/or condition of the features.
Spectral Signatures
Certain wavelengths where the curves will be absorbed and reflected
Spectral Signatures
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)
Spectral Reflectance and spectral emitting (for wavelengths greater than 3.0 micrometer) are referred to in this manner
Spectral Signatures
Peaks at the graph are called
Spectral pattern
Sudden rise in peaks in the graph
Typical red edge
Present in all healthy vegetation
Chlorophyll reflectance
Valleys in the graph
Absorption
Used as benchmark for vegetation stress
Red Edge
0.8 nm to 1.4 nm (due to cell structure of vegetation)
Chlorophyll reflectance
Factors that affects the spectral patterns
- temporal effects
- spatial effects
Spectral curves that can ID materials in certain spectral regions only
Spectral response patterns
Spectral response that allows assessment of type/conditions of features
Spectral signatures
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
Differences of the same type of features from different geographical locations
Spatial effects
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
Any factors that change the spectral characteristics of a feature over time
Temporal effects
What happens to the spectral patterns of plants during RAINY SEASON?
Water absorption valley will be more defined. Dominant green colors
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
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
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
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
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
- Attenuates (reduces) energy from the sun
- 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
- <incidence = <reflection
- wavelength < surface height variations
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
