Revised L5 TM Radiometric Calibration Procedures and

Revised L5 TM Radiometric Calibration Procedures and Postcalibration Dynamic Ranges

Gyanesh Chander (SAIC/EDC/USGS) Brian Markham (LPSO/GSFC/NASA)

U.S. Department of the Interior U.S. Geological Surv ey

Outline      

Background Radiometric Calibration Procedure Radiometric Calibration Modification Impacts of the radiometery updates on Landsat data users L5 TM absolute calibration accuracy relative to L7 ETM+ Summary

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History of Landsat 5 (L5) TM    

L5 was developed by the NASA and launched in March 1, 1984 After on-orbit check out, it was initially operated by the NOAA In September 1985, operation of L5 was turned over to a private company, Earth Observation Satellite Company (EOSAT), now known as Space Imaging In July 2001, the still-operational L5 and its entire image archives were turned back over to the U.S. government to be operated by the USGS

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TM Optical Layout

4

L5 TM Spectral Coverage and Ground Sample Distance (GSD)

5

History of L5 TM Processing System  Over the lifetime of L5, there have been three U.S. data   

product generation systems The initial processing system for L5 was the TM Image Processing System (TIPS)  It was used by NOAA, and later EOSAT adopted it EOSAT updated their processing system to the Enhanced Image Processing System (EIPS) in October 1991 At the same time, the USGS began its own TM archive, and it has always processed TM data with the National Landsat Archive Production System (NLAPS)

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Radiometric Calibration procedure    

Historically, the radiometric calibration procedure for this imagery used the instrument's response to the IC on a scene-byscene basis to determine the gain and offset of each detector The reflective band calibration algorithm for in-flight data regresses the lamp responses against the prelaunch radiances of the lamp states The slope of the regression represents the gain and the intercept represents the bias After more than 20 years of service, the L5 TM continues to operate well



Nevertheless, the instrument has aged and its characteristics have changed since launch

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L5 TM detector response over lifetime Lamp Behavior

Detector Response



Research has shown that the method of radiometric calibration used to date by NLAPS (and TIPS) systems has been degraded by changes over time in the instrument’s IC

8

Life Time Gain Plot for L5 TM (Band-3)

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Cross-calibration of the L7 ETM+ and L5 TM sensors based on tandem data sets

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Radiometric Calibration Modification 

   

The new procedure for the reflective bands (1-5,7) is based on a lifetime radiometric calibration curve for the instrument derived from the instrument’s internal calibrator (IC), cross-calibration with the ETM+, and vicarious measurements For bands 5 and 7, detector responses were corrected for variation due to the buildup of an ice film on the cold focal plane window Thus, time-dependent calibration look-up tables (LUT) were generated from the lifetime gain model equations for all bands Simultaneous with this change, the biases are now applied line-byline based on the dark shutter responses acquired from each scan line and the regression based offset will be discarded The thermal band will continue to be calibrated using the IC

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Comparison of L5 TM Radiometric Calibration Methods

L5 TM data processed at IGS



Warning: Other processors in the US and in the rest of the world have not necessarily implemented the LUT, so recent L5 TM images available from various facilities and web sites are not necessarily reliable or consistent with USGS radiometrically

Identifying IC vs. LUT Products  Processing date  After May 5, 2003 = LUT  Before May 5, 2003 = IC  Revised product report naming convention.  RADIOMETRIC CORRECTION  Algorithm (IC): NASA  Algorithm (LUT): NASA CPF  Revised postcalibration dynamic ranges

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Conversion to Radiance for Level 1 products   

Calculation of radiance is the fundamental step in putting image data from multiple sensors and platforms into a common radiometric scale Conversion from calibrated digital numbers (Qcal) in L1 products back to at-sensor spectral radiance (Lλ) requires knowledge of the original rescaling factors The following equation is used to perform a Qcal-to-radiance conversion for a L1 product:

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L5 TM Postcalibration Dynamic Ranges

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Radiance to TOA Reflectance  

A reduction in between-scene variability can be achieved through a normalization for solar irradiance by converting the spectral radiance, to a planetary or exoatmospheric reflectance When comparing images from different sensors, there are two advantages to using reflectance instead of radiances

 



First, the cosine effect of different solar zenith angles due to the time difference between data acquisitions can be removed, Second, it compensates for different values of the exoatmospheric solar irradiances arising from spectral band differences

The combined surface and atmospheric reflectance of the Earth is computed according to:

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Solar exoatmospheric spectral irradiances (ESUNλ)

 ESUNλ using the CHKUR solar spectrum in MODTRAN 4.0  This spectrum is being used for L7 ETM+ and is believed to be an improvement  

over the spectra used for previously presented L4/L5 TM solar irradiance values The primary differences are in bands 5 and 7 For comparisons to other sensors, users need to verify that the same solar spectra are used for all sensors

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Impacts of the radiometery updates on Landsat data users  L5 TM data are now scaled differently     



This change will improve absolute calibration accuracy, consistency over time and consistency with L7 ETM+ data Programs with hard coded LMIN and LMAX will not work correctly without change Land cover users doing visual interpretation (e.g., trends) or general classification, the calibration changes may not be a major concern Analyses that were based on specific DN thresholds (e.g., Tasselled Cap) will need to be adjusted, but the thresholds should now work more consistently over the mission life Users should note that products generated before May 5, 2003 and converted to radiance using older LMINs and LMAXs will not provide the same radiances as those processed since May 5, 2003 and converted to radiance with the new LMINs and LMAXs L4 TM still uses old procedure and LMIN and LMAX

L5 TM absolute calibration accuracy relative to L7 ETM+  This section provides comparison of the reflectance 

measurements obtained from the “tandem” L5 TM and L7 ETM+ scenes The goal of this analysis is to show the improvement in consistency of the L5 with L7 imagery achieved by implementation of the LUT (instead if IC) approach in L5 data product generation

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Process raw data to Level 1 products L7 ETM+

L5 TM

Q

Q

Qcal(IC) IAS

Qcal(LUT) NLAPS

Lcal=Grescale*Qcal+Brescale L

Lcal(IC)

Lcal(LUT)

L5 TM and L7 ETM+ tandem image pairs

L5 TM and L7 ETM+ Relative Spectral Response (RSR) Profiles ETM+ and TM RSR (Band-1) alpha=0.778 L7

0.9

L5

0.8

0.7

0.7

Normalized RSR

0.8

0.6 0.5 0.4 0.3

0.46

0.48

0.5

0.52

0.54

0 0.48

0.56

0.4 0.3

0.5

0.52

0.54

0.56

0.58

0.6

0.62

0.64

0 0.56

0.66

0.58

0.6

0.62

0.64

0.7

0.6 0.5 0.4 0.3

L5

0.8

0.5 0.4 0.3 0.2

0.1

0.1 0.92 0.94 0.96

0.9

0.6

0.2

0.9

L7

Normalized RSR

0.8

0.7

Normalized RSR

0.8

0 1.46

0.7

0.72

0.74

0.76

1

0.9

L5

0.68

ETM+ and TM RSR (Band-7) alpha=0.817

1

0.9

0.66

Wavelength

ETM+ and TM RSR (Band-5) alpha=0.755 L7

Wavelength

0.5

Wavelength

1

0.82 0.84 0.86 0.88

0.6

0.1

ETM+ and TM RSR (Band-4) alpha=0.877

0.8

L5

0.2

Wavelength

0 0.72 0.74 0.76 0.78

L7

0.7

0.3

0.1 0.44

0.8

0.4

0.1 0.42

L5

0.5

0.2

0.4

0.9

0.6

0.2

0

L7

Normalized RSR

0.9

Normalized RSR

1

1

1

Normalized RSR

ETM+ and TM RSR (Band-3) alpha=0.847

ETM+ and TM RSR (Band-2) alpha=0.761

L7 L5

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

1.52

1.58

1.64

1.70 Wavelength

1.76

1.82

1.88

1.94

1.96

2

2.04 2.08 2.12 2.16

2.2

2.24 2.28 2.32 2.36

Wavelength

2.4

2.44

TOA Reflectance Obtained in ETM+ vs. TM (Band-1) 0.19 0.18

TM Reflectance

0.17

1x1 Line TM (IC) NIOB TM (LUT) NIOB TM (IC) RVPN TM (LUT) RVPN TM (IC) DC TM (LUT) DC

0.16 0.15 0.14 0.13 0.12 0.11 0.1 0.09 0.09

0.11

0.13

0.15

ETM+ Reflectance

0.17

0.19

L5 TM % difference relative to L7 ETM+ (Band 1)

% Difference (TM-ETM+)/ETM+

4

0 0.09

0.11

0.13

0.15

0.17

0.19

-4

-8

-12

TM (IC) NIOB TM (LUT) NIOB TM (IC) RVPN TM (LUT) RVPN TM (IC) DC TM (LUT) DC

-16

ETM+ Reflectance

The percentage mean difference in reflectance measurements obtained from the L5 TM relative to ETM+ in band-1 is reduced from about 9.5% (using IC) to 1.3% (using LUT)

TOA Reflectance Obtained in ETM+ vs. TM (Band-2) 0.2

TM Reflectance

0.18

1x1 Line TM (IC) NIOB TM (LUT) NIOB TM (IC) RVPN TM (LUT) RVPN TM (IC) DC TM (LUT) DC

0.16 0.14 0.12 0.1 0.08 0.06 0.06

0.08

0.1

0.12

0.14

0.16

0.18

L5 TM % difference relative to L7 ETM+ (Band 2)

0.2

8

ETM+ Reflectance

The percentage mean difference in reflectance measurements obtained from the L5 TM relative to ETM+ in band-2 is reduced from about 15.6% (using IC) to 1.8% (using LUT)

% Difference (TM-ETM+)/ETM+

4 0 0.06 -4

0.08

0.1

0.12

0.14

0.16

0.18

-8 -12 -16

TM (IC) NIOB TM (LUT) NIOB TM (IC) RVPN TM (LUT) RVPN TM (IC) DC TM (LUT) DC

-20 -24

ETM+ Reflectance

0.2

TOA Reflectance Obtained in ETM+ vs. TM (Band-3) 0.24 0.22

TM Reflectance

0.2 0.18

1x1 Line TM (IC) NIOB TM (LUT) NIOB TM (IC) RVPN TM (LUT) RVPN TM (IC) DC TM (LUT) DC

0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.04

0.08

0.12

0.16

0.2

8

% Difference (TM-ETM+)/ETM+

ETM+ Reflectance

The percentage mean difference in reflectance measurements obtained from the L5 TM relative to ETM+ in band-3 is reduced from about 10.8% (using IC) to 2.6% (using LUT)

L5 TM % difference relative to L7 ETM+ (Band-3)

0.24

4 0 0.04

0.08

0.12

0.16

0.2

-4 -8 -12 TM (IC) NIOB TM (LUT) NIOB TM (IC) RVPN TM (LUT) RVPN TM (IC) DC TM (LUT) DC

-16 -20

ETM+ Reflectance

0.24

TOA Reflectance Obtained in ETM+ vs. TM (Band-4) 0.38 0.36

TM Reflectance

0.34 0.32 0.3

1x1 Line TM (IC) NIOB TM (LUT) NIOB TM (IC) RVPN TM (LUT) RVPN TM (IC) DC TM (LUT) DC

0.28 0.26 0.24 0.22 0.2 0.18 0.18

0.22

0.26

0.3

0.34

0.38

The percentage mean difference in reflectance measurements obtained from the L5 TM relative to ETM+ in band-4 is reduced from about 7.4% (using IC) to 1.3% (using LUT)

% Difference (TM-ETM+)/ETM+

ETM+ Reflectance

L5 TM % difference relative to L7 ETM+ (Band-4) 4

0 0.18

0.22

0.26

0.3

0.34

-4

-8

TM (IC) NIOB TM (LUT) NIOB TM (IC) RVPN TM (LUT) RVPN TM (IC) DC TM (LUT) DC

-12

-16

ETM+ Reflectance

0.38

Summary 



Effective May 5, 2003, L5 TM data processed and distributed by the USGS/EDC was radiometrically calibrated using a new procedure and revised calibration parameters  The modified calibration approach no longer uses the IC gain on a scene-by-scene basis for calibration of the reflective bands  Calibration of reflective band image data was implemented through a time-dependent calibration LUT  Users will need to use new postcalibration dynamic ranges to convert the calibrated data products to radiance It is believed that full implementation of these processing changes will lead to a superior L5 TM data product that will be comparable to L7 ETM+ radiometery, and will provide the basis for continued longterm studies of the Earth’s land surfaces

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Contact Information

Gyanesh Chander SAIC/EDC/USGS Phone: 605-594-2554 Email: [email protected]

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