Appendix B - Calibration Parameter File (CPF) Content
B.1 File Content
The CPF supplies the radiometric and geometric correction parameters required during Level-1 processing to create superior products of uniform consistency across the Landsat 7 system. Besides the file attributes, these parameters fall into one of three major categories: geometric parameters, radiometric parameters, or artifact removal parameters.
B.2 Geometry Parameters
The geometric parameters are classified into 11 first tier groups. The heading for each group is the actual ODL group name used in the CPF.
- Earth Constants
- Orbit Parameters
- Scanner Parameters
- Spacecraft Parameters
- Mirror Parameters
- Bumper Mode (April 1, 2007)
- Scan Line Corrector
- Focal Plane Parameters
- Attitude Parameters
- Time Parameters
- Transfer Function
UT1 Time Parameters
B.3 Radiometric Calibration Parameters
The radiometric parameters are classified into 15 first tier groups. A brief description of each group and their use in various Landsat 7 systems or by an individual user follows. The heading for each group is the actual ODL group name used in the CPF.
- Detector Status
The Detector Status parameters provide a five-element code that describes the current health status of each ETM+ detector. The five codes indicate detector status (live or dead), low gain signal noise, high gain signal noise, low gain dynamic range quality, and high gain dynamic range quality.
- Detector Gains
Analysis of the SIS calibration transfer to the Internal Calibrator (IC) and output from the Combined Radiometric Model (CRaM) used by IAS results in the Detector Gain parameter set. For each detector, there is a pre-launch gain, post-launch gain, and a current gain for each of the two gain settings. The pre-launch and post-launch gains are based on the SIS calibration and remain static while the current gain is updated as a function of CRaM improvement and detector responsivity over time. The Detector Gain parameters are used to radiometrically correct ETM+ data prior to LPS processing and derivation of the Automatic Cloud Cover Assessment (ACCA) score and optionally used by LPGS as an alternative to computing gains on the fly from the IC data.
- Bias Locations
The bias location parameters refer to the IC data. They specify the starting pixel location for the bias (dark current restore), the length in pixels of the bias region, and the length of useable IC data including the pulse. A set of parameters exists for each of the three band groups - reflective, panchromatic, and thermal. They are used during radiometric correction for rapid retrieval of calibration pulse and shutter data.
- Detector Biases Band 6
During Level-1 processing, Band 6 biases are generally computed from the IC for the image being processed. This is a complex task and may be subject to anomalies. This parameter group is computed both prelaunch and at regular intervals over the life of the mission. These are baseline Band 6 biases and are used during Level-1 processing if the image specific IC-derived biases prove unreliable.
- Scaling Parameters
The Scaling Parameter set consists of the lower and upper limit of the post- calibration dynamic range for each band in each gain state. These are the LMIN and LMAX values and are expressed in units of absolute spectral radiance. These values are used by LPGS to convert 1G products to scaled 8-bit values and by users for the reverse transformation. There is an LMIN / LMAX pair per band for each of the gain modes.
- MTF Compensation
All image systems, including Landsat 7, cause a blurring of the scene radiance field during image acquisition. Accurate characterization of this blurring is referred to as the MTF. Restoration processing compensates and corrects for systemic degradations to yield greater radiometric accuracy. The MTF compensation parameters are weighting functions for each band. Five weighting parameters for both pixel and line directions were selected to best fit the optimal MTF response. These are applied to the components of the piecewise cubic convolution kernel to generate the optimal MTF reconstruction kernel.
- Sensitivity Temperatures
The temperature of the detectors on the primary focal plane of the ETM+ is not controlled and tends to warm up as the instrument operates. The cold focal plane is controlled but may operate at different set points. Most detectors show some dependence of responsivity with temperature. The sensitivity temperature parameters describe the relationship between gain change and operating temperature for each detector and are used to adjust the gains derived from multi-calibration sources. Gains derived solely from IC data are not temperature adjusted.
- Reference Temperatures
The sensitivity temperature coefficients are used to adjust gains for varying focal plane temperatures. The reference temperatures are used to normalize the gains to a stable temperature. A single reference temperature is calculated prelaunch and post launch for each band at both gain states.
- Lamp Radiance
The lamp radiance parameters contain the actual radiance of the two IC lamps in three possible configurations (i.e. lamp 1 on - lamp 2 off, lamp 1 off - lamp
2 on, lamp 1 on - lamp 2 on). For each reflective band there are pre-launch, post-launch, and current values for the low and high gain settings. Pre-launch values are established by transferring the SIS calibration to the IC lamps within the ETM+. Post-launch is determined using PASC and FASC calibration data. The lamp radiance parameters used to compute the gains are used for converting raw ETM+ data to units of absolute radiance.
- Reflective IC Coefficients
Radiance levels produced by the IC, or seen by the detectors vary as a function of instrument state. Several parameters affecting instrument state are tracked and used for correcting this effect. These parameters are instrument on time, position on-orbit, and temperatures of the IC components and focal plane arrays. The reflective IC coefficients are used in the model that corrects for these effects. For each detector there are 18 coefficients for both the low and high gain states.
- Lamp Reference
The radiance levels produced by the IC, or seen by the detectors vary as function of instrument state. The model that compensates for these effects requires as input 14 temperatures of the IC components and focal plane arrays. In general, these temperatures are extracted from the PCD for the image being processed. However, the IAS also performs a pre-launch calibration of the ETM+ and a post calibration using the combined radiometric model. The lamp reference parameters represent the instrument state at the time of calibration.
- Band 6 View Coefficients
The Band 6 view coefficients are used in computing the actual shutter (i.e. bias) values when processing the emissive IC data. The offset algorithm takes into account radiance of the shutter flag as well as contributions from other instrument components such as the scan mirror and SLC. Each Band 6 detector has a different view of the contributing components. The Band 6 view coefficients capture this view and are used to adjust the contributing spectral radiances accordingly.
- Band 6 Temp Model Coefficients
The Band 6 temperature coefficients are used to calculate the temperature of the scan mirror. The emissive IC algorithm requires scan mirror temperature for computing Band 6 gains and offsets. The scan mirror's contribution to the Band 6 response must be calculated and accounted.
- Lamp Current Coefficients
Included in the PCD are the currents for the two IC lamps. The currents are in a raw data format and require conversion to engineering units (i.e., milli-amps) prior to their use. The lamp coefficient parameters are used to linearly transform the raw counts to milli-amps. There are two coefficients for each lamp.
- Thermistor Coefficients
Included in the PCD are a variety of ETM+ component temperatures. The temperatures are in a raw data format and require conversion to valid numbers prior to their use. The thermistor coefficients parameters are used for this purpose. Six conversion coefficients are supplied for each of the 28 different temperatures that accompany the PCD.
B.4 Artifact Removal Parameters
The artifact parameters are classified into 9 first tier groups. A brief description of each group and their use in various Landsat 7 systems follows. The heading for each group is the actual ODL group name used in the CPF. Not all the following issues impact ETM+ data but the CPF is designed to accommodate them if the need arises.
- Memory Effect
Memory effect is a noise pattern commonly known as banding. It can be identified as alternating lighter and darker horizontal scan-wide stripes. The memory effect parameters were derived by the IAS and are static. They consist of a magnitude and time constant for each detector. These are used in an inverse filtering operation to remove the memory effect artifact.
- Ghost Pulse
The ghost pulse is a faint secondary image of the IC lamp pulse. It appears in Band 5 and Band 7. The ghost pulse parameters identify the beginning and ending minor frames that bound this ghost image.
- Scan Correlated Shift
Scan correlated shift is a sudden change in bias that occurs in all detectors simultaneously. The scan correlated shift parameters are derived by the IAS and are static. They consist of a bias magnitude for each detector and are used to compensate for the shift when it occurs.
Striping is defined as residual detector-to-detector gain and offset variations within a band of radiometrically corrected (Level 1R) data. The 1R process is intended to remove detector-to-detector variations through the generation of relative gains and bias from histograms. These are included in the absolute gains and biases eventually applied. Nonetheless, the possibility of residual striping remains. The striping parameters are correction methodology flags. Two processing options are possible: linearly adjust the 1R data to match the means and standard deviations of each detector to a reference detector or to an average of all the detectors. There is one striping parameter per band for each of the gain modes.
Histogram analysis estimates the relative gains and biases for all detectors by characterizing the response behavior of individual detectors in a band relative to the other detectors in a band. Results are used to adjust the gains and biases applied during radiometric correction. The histogram parameters control the algorithm by specifying detector noise, a normalization reference detector for each band, saturation metrics, and histogramming window size.
- Impulse Noise
Impulse noise within a digital signal manifests itself in a sample as a departure from the signal trend far in excess of that expected from random noise. The impulse noise parameters specify a median filter width and an impulse noise threshold for each detector. The IAS employs these parameters for identifying and trending impulse noise in otherwise homogeneous data such as night scenes and FASC imagery.
- Coherent Noise
Coherent noise is a low-level periodic noise pattern found in all Landsat 5 imagery and characterized by the IAS for Landsat 7. The coherent noise parameters consist of the number of noise components and a set of waveform characteristics that describe each component for each band. The waveform characteristics are the mean, sigma, minimum, and maximum for each component's frequency, phase, and magnitude.
- Detector Saturation
In addition to normally observed saturation (i.e., 0, 255) two other types of detector saturation can occur. An analog to digital converter may saturate below 255 counts at the high end, or above 0 at the low end. The detector saturation parameters identify these levels for each detector. The analog electronic chain may saturate at a radiance corresponding to a level below 255 counts and above 0 counts on the low end. The detector saturation parameters also identify these levels for each detector.
- Fill Patterns
LPS uses two values to fill minor frames to distinguish missing or bad band data from good data. The two fill values used are zeros for odd detectors and 255s for even detectors. The fill data are placed on a minor frame basis - if data are missing from part of a minor frame, the whole minor frame is filled. The alternating 0/255 fill pattern was selected to unambiguously flag artificial fill from reflectance values that naturally could occur such as those caused by SLC-off.
B.5 ACCA Parameters
Each scene processed by LPS undergoes ACCA prior to being archived. The cloud cover scores become searchable metadata and can be used to filter out undesirable scenes during an archive search. The ACCA algorithm uses a variety of threshold and band indices for cloud identification. These may change during the mission and are therefore included in the CPF.
- ACCA Biases
The LPS ACCA algorithm requires radiometrically corrected image data. The ACCA Biases parameter set is used in conjunction with the Detector Gains for converting raw DNs to units of absolute radiance. There is one bias parameter per detector per band for each of the two gain modes. Although ACCA uses only Band 2 through Band 6, the other band biases are included for completeness. Biases are reported in units of digital counts.
- ACCA Thresholds
The LPS ACCA algorithm uses Band 2 through Band 6 in a combination of thresholds, ratios, and indices to separate clouds from land. Results are reported in metadata that are eventually used in client data searches. LPS and possibly IGS list the ACCA Threshold parameters in the CPF for use by the end user.
- Solar Spectral Irradiances
The LPS ACCA algorithm converts radiometrically-corrected data to units of planetary reflectance prior to cloud filtering. This involves normalizing image data for solar irradiance, which reduces between-scene variability. The parameter values listed in Table B-1 are the mean solar spectral irradiances for Band 1 through Bands 5, 7 and 8. There is one value for each band.
|Band||Watts /(m² * µm)|
Table B-1. Solar Spectral Irraidances
- Thermal Constants
ACCA converts Band 6 from spectral radiance to a more physically useful variable, namely the effective at-satellite temperatures of the viewed Earth-atmosphere system. The transformation equation requires two calibration constants, which are listed in Table B-2.
|K1||666.09||(Watts/(m² * sr * µm))|
Table B-2. ETM+ Thermal Constants