Analyze Radiance

ERDAS IMAGINE Help

HGD_Variant
16.5.2
HGD_Product
ERDAS IMAGINE
HGD_Portfolio_Suite
Producer

Category: Surface

AnalyzeRadianceOperator

Description

Given time of day and calendar date, the operator provides output in radiance units (Watt per meter squared) for each elevation pixel using its local slope and aspect, computing either insolation (incident solar/lunar irradiance) or terrestrial radiation (reflected radiance from a surface with known dominant reflectance coefficient), with or without including light viewshed that blocks direct beam irradiance. Insolation is computed using medium fidelity models of radiative energy transfer through the atmosphere and ground radiation. Algorithm considers atmosphere (based on standard pressure of average DEM elevation) for both light refraction and light scatter (Rayleigh and Mie). Algorithm considers ground as a secondary source of illumination from terrestrial radiation such that total energy incident on any surface (defined by its local normal) is composed from 3 parts - direct beam irradiance, diffuse radiation (skylight), and ground albedo (neighborhood terrain illuminates any non-horizontal surface). Algorithm employs efficient polynomial models for earth curvature when elevation grid footprint exceeds certain limits, which allows producing realistic illumination over very large geographic areas.

Connections

Name

Objects Supported

Description

Shown by Default

Required

Default Behavior or Behavior if not Required

DEMRaster

IMAGINE.Raster

Digital elevation model raster.

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DateTime

IMAGINE.DateTime

Specifies the date and time information needed to calculate (in a combination with time duration parameter) the sun angle and intensity for each time slot. The date and time value is specified in UTC

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TimeDurationHours

IMAGINE.Unsigned

Optional count of extra hours in the time interval for computing average radiance or light viewshed opacity mask. Valid range is from 0 to 15.

0

RadianceMapType

IMAGINE.String

Type of radiance map: {"Insolation","Radiation","Shaded Insolation", "Shaded Radiation","Light Viewshed"}.

"Insolation"

GroundReflectance

IMAGINE.Double

Reflectance coefficient between 0.01 and 1.0 for dominant surface cover. Default is in between vegetation and pale soil (dry grass)

0.25

AirVisibilityKm

IMAGINE.Double

Meteorological visibility of the atmosphere in kilometers affecting diffuse skylight and direct beam attenuation.

10.0

HeightVisualScale

IMAGINE.Double

Vertical exaggeration coefficient for light viewshed (shadow casting) only.

1.0

RadianceUnitScale

IMAGINE.Double

Additional scale for radiance output (e.g., use 0.001 for output in kW/m^2)

1.0

RadianceRaster

IMAGINE.Raster

Raster generated from the specified process. For "Light Viewshed" type of radiance map, output pixels represent the amount of time in hours under the light source, Sun or Moon. Output pixels for other types represent the average intensity of incident or reflected energy flux in units of radiance (Watts per meter squared multiplied by the unit scale factor). For each pixel, the light viewshed mask for shaded insolation or radiation is used to block the direct beam component of total radiance in each time epoch under the shadow.

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Related Operators

Example Model

Below is an example of the Analyze Radiance operator used in Shadow Analysis model

AnalyzeRadiance-ShadowsModel