EOIR Radiometric Properties

Use to define the radiant energy measurement properties.

Units for Saturation and Sensitivity

Irradiance. The Sensitivity and Dynamics Range parameters operate in irradiance units (W cm^-2). Irradiance is better suited for sensors that are observing point sources like stars.

Radiance. The Sensitivity and Dynamics Range parameters operate in radiance units (W cm^-2 sr^-1). Radiance is better suited for sensors that are observing resolved images, where object shapes are discernible.

Simulate Saturation. Pixels can only measure up to the specified saturation level of radiant signal. This is the way physical detectors would behave.

Saturation defines the "brightest" signal that the sensor can measure.

Simulate Quantization. Performs the analog to digital conversion of the output image.

Radiometric parameter input mode. Specify which radiometric parameters to use. The options are high level or low level.

High Level Parameters

Sensitivity. Sensitivity defines the "noise floor" of the sensor. It is not possible to detect signals below this level.

Dynamic Range. Dynamic Range is the ratio of the brightest signal to the noise floor.

Editing Sensitivity and Saturation Data

The following edit tables are used to represent sensor performance and can be populated with measurements from an actual sensor or estimates for a sensor being developed. An edit dialog is displayed that enables you add a new sensitivity or saturation time pair or modify an existing one.

You can edit data for any of the following sensitivity or saturation time pairs:

Noise Equivalent Irradiance (NEI) vs. Integration Time.
Noise Equivalent Radiance (NER) vs. Integration Time.
Saturation Equivalent Irradiance (SEI) vs. Integration Time.
Saturation Equivalent Radiance (SER) vs. Integration Time.

Low Level Parameters

Quantum Efficiency mode. The method of specifying the Quantum Efficiency (QE) value.

Spectral QE file. The SRF-formatted spectral profile of QE values.

QE. The spectrally flat band effective QE value.

Detector fill factor. The portion of the detector area that is photosensitive.

Read noise. The RMS number of the electrons-per-pixel noise from reading out the charge.

Dark current rate. The average rate of accumulated dark noise per detector.

Analog to Digital Conversion

Analog to digital conversion mode. The method of specifying the analog to digital quantization. There are four options: bit-depth and noise, bit-depth and QSS (quantization step size), full-well and noise, and full-well and QSS.

Full-well capacity. The maximum number of electrons per detector where a detector will saturate.

Digital bit depth. The number of bits to quantize the dynamic range of the signal into digital counts.

Quantization step size. The number of electrons per digital count in the quantized digital output.

Specifying an Integration Time

When preparing to take measurements with the sensor model, you specify an Integration Time. This is the time interval over which a radiant signal is collected before generating an image. The longer the time, the more photons get collected. This field is equivalent to the "exposure time" setting on an old analog film camera.

The sensor model uses the Integration Time to interpolate into the Edit tables to compute Dynamic Range and NEI/NER and SEI/SER. In the case where the selected Integration Time is outside of the bounds of numbers entered in the table or there was only a single point entered, a physics based approximation is used to extrapolate Dynamic Range, NEI/NER and SEI/SER.

For additional information, see the EOIR Model Description and Validation document.