# Presentation: 193260

## Consistent Radiometric Calibration of 

- Consistent Radiometric Calibration of
- Landsat TM and MSS Sensors

- Landsat Science Team Meeting
- January 7, 2008
- Fort Collins, CO
- Dennis Helder
- South Dakota State University

## Outline

- Introduction
- Pseudo-Invariant Calibration Sites (PICS)
- Landsat-4 TM Radiometric Calibration
- MSS Radiometric Calibration
- Cross-Calibration of MSS sensors
- Landsat-1 to Landsat-2
- Landsat-2 to Landsat-4
- Landsat-3 to Landsat-4
- Landsat-4 to Landsat-5
- Validation of Cross-calibration results
- Cross-calibration of Landsat-5 MSS to Landsat-5 TM
- Summary & Open Issues
- Acknowledgements:
- Funding by NASA GSFC & USGS EROS
- EROS for several hundred Level 0 MSS and TM scenes
- IP Lab staff:  Rajendra Bhatt, Sirish Uprety, Jim Dewald,
- 	LukeWeyer

## Pseudo-Invariant Calibration Site (PICS)

- Pseudo-invariant calibration sites are temporally and spatially stable natural ground targets that are ideally bright, spatially homogeneous, spectrally flat, and are generally located in arid regions.
- Pseudo-invariant sites can be used to
- Monitor long term radiometric gain of satellite sensors (e.g. Landsat-5 TM)
- Cross-calibrate multiple satellite sensors that are unable to take image data from the same ground target under simultaneous conditions
- However, the use of this technique requires adequate data collection from invariant sites on a repetitive basis.
- Key pseudo-invariant sites frequently used for Landsat cal-val are: *Libya-4 desert (P181R40) and Sonoran desert (P38R38).*

**Notes:**
Consider these two slides (previuos/current) and rewrite to state the purpose/concept first, then the procedures...  Can we say anything quantitative in this introduction—ie. What level of precision can be expected with this technique?

## PICS for cross-calibration of L4 TM and L5 TM

- Limited near coincident PICS collects available for L4 and L5 TM
- Cross-calibration at several points in time was achieved through use of PICS from Egypt, Sonoran Desert, Iraq, Algeria, and Libya.

- Egypt (path 179 row 41)

- Yuma, Arizona (path 38 row 38)

- Iraq (path 166 row 39)

- Algeria (path 192 row 39)

- Libya (path 182 row 42)

## Sonoran Desert: An invariant site in North America 

- Large African pseudo-invariant desert sites are considered to be the optimal sites in the world for sensor calibration.
- Many satellite sensors have a limited
- 	archive of data from these sites.
- Sonoran desert (on the Mexican American border) was found to have invariant regions comparable to the Saharan desert.
- The lifetime response of L5 TM to these regions agree with LUT07 calibration model to within **1-2% in the visible and 2-3% in the SWIR.**

- The most invariant regions
- in Sonoran Desert

**Reference:** Daniel L. Morstad, Dennis L. Helder, “*Use of pseudo-invariant sites for *
*long-term sensor calibration*”, IGARSS 2008

## Radiometric formulation

- MSS data in the USGS archive is already radiometrically processed based on internal calibration system.
- The calibrated pixels (QCAL) can be converted to at-sensor radiance (Lλ) and top-of-atmosphere (TOA) reflectance (ρ) using the following equations:
- 	where,
- LMINλ and LMAXλ are known as post-calibration dynamic ranges and their values are given for all five MSS sensors
- d = Earth-sun distance in astronomical units (AU),
- ESUNλ= mean solar exoatmospheric spectral irradiances, and
- θ = solar zenith angle for the image portion of interest

## Landsat-1 to -7 Characteristics

| Satellite | Launched | Decommissioned | Sensors | Orbit |
| --- | --- | --- | --- | --- |
| Landsat-1 | July 23, 1972 | January 6, 1978 | RBV*, MSS | 18 days/900 km |
| Landsat-2 | January 22, 1975 | February 25, 1982 | RBV, MSS | 18 days/900 km |
| Landsat-3 | March 5, 1978 | March 31, 1983 | RBV, MSS | 18 days/900 km |
| Landsat-4 | July 16, 1982 | June 15, 2001 | MSS, TM | 16 days/705 km |
| Landsat-5 | March 1, 1984 | Still Alive after
almost 25 years | MSS, TM | 16 days/705 km |
| Landsat-6 | October 5, 1993 | Failure upon launch | ETM | 16 days/705 km |
| Landsat-7 | April 15, 1999 |  | ETM+ | 16 days/705 km |

- *The RBV (Return Beam Vidicon) cameras did not achieve the popularity
-   of the MSS sensor

**Notes:**
Add flashy graphic about Landsat 5 still alive after almost 25 years!

## L4 TM to L5 TM Cross-Calibration

## L4 TM Cross-Cal Key Issues

- Absolute Cross-calibration to Landsat 5 TM
- Original work from Iraq and Sonora sites in 1990; approximately 2% uncertainty.
- Updated with data from Egypt (1987), Libya (P182R42, 1988), approx. 2% uncertainty
- Consistent story from all data sources
- Consistent story across bands
- Use of Iraq as trending site due to First Gulf War
- Lack of sufficient PICS data for trending purposes
- Gap in instrument operation from 1984 -- 1987

## Key Issues (cont.)

- Use of L5 long term trends to model L4
- Quickly dismissed; no similarities
- Reluctance to depend significantly on IC due to experience with Landsat 5 TM
- Limited use due to lack of IC data for pre-gap model
- IC post-gap model essentially mirrors L5—limited use
- Appropriate use of absolute/relative data sources
- Ranking of data wrt to confidence level
- Combination of absolute and relative models to provide update to post-gap recommendation

## Procedure Followed for L4 Calibration

- Accept cross-calibration with L5 as absolute anchor point at essentially two points in time
- Internal consistency on the order of 2%
- Reject obvious outlier
- Accept Libya-4 and Sonora trending data
- Proven consistency at 3% or less
- Anchor at absolute cross-cal dates
- Accept pre-gulf war Iraqi sites
- Use as additional trending data
- Reject all post-gulf war Iraqi data (excessive uncertainties)
- Fit appropriate (i.e. simple!) mathematical model for LUT

## L4 TM Band 1

## L4 TM Band 1 – NLAPS Comparison 

- Approximately 6% change from NLAPS

## L4 TM Band 2

## L4 TM Band 2 – NLAPS Comparison 

- Approximately 6% change from NLAPS

## L4 TM Band 3

- Sonora data suggest possible change in gain, up to 4%
- Recall Sonora only provides trend information, so max change is ±2%--within uncertainty of the measurement.

## L4 TM Band 3 – NLAPS Comparison 

- Approximately 8% change from NLAPS

## L4 TM Band 4

- Sonora uncertainty in Band 4 = 2.5%
- Only 2% range in Sonora data points

## L4 TM Band 4 – NLAPS Comparison 

- Approximately 3.5% change from NLAPS

## L4 TM Band 5

- No Libya data available for band 5
- Sonora uncertainty = 3%
- Only two data points available with ±2.5% indicated

## L4 TM Band 5 – NLAPS Comparison 

- Approximately 7% change from NLAPS
- Note: wrt peaks of outgassing cycles.

## L4 TM Band 7

- Note consistency of all trending data: <1% change indicated

## L4 TM Band 7 – NLAPS Comparison 

- Approximately 2% change from NLAPS
- Note: wrt peaks of outgassing cycles.

## L4 TM Gain Recommendations

| Band | Gain | Uncertainty | Difference from NLAPS |
| --- | --- | --- | --- |
| 1 | 3.95x10-5DSL + 1.49 | ±2% | 6% |
| 2 | 0.719 ± 0.005 | ±1% | 6% |
| 3 | 0.954 ± 0.008 | ±2% | 8% |
| 4 | 1.073 ± 0.015 | ±2% | 3-5% |
| 5 | 7.708 ± 0.375 | ±5% | 7% |
| 7 | 14.65 ± 0.266 | ±2% | 2% |

## Lifetime Radiometric Calibration Stability and Consistency of Landsat-1 through -5 MSS Sensors

## Methodology

- Good quality and cloud free scenes from Sonoran Desert were searched for all 5 MSS sensors.
- Varieties of scenes used: MSS-X, MSS-P, and MSS-A
- TOA reflectance values were derived for the specified 250*250 pixel (MSS-X/A) ROI for all scenes.
- A lifetime instrument response was derived by plotting TOA reflectance against time for each sensor.

- 250*250 pixels ROI

- Atmospheric and BRDF effects are not accounted for initially.

## Results: Band 1

- Radiometric calibration of MSS sensors show good stability over lifetime.
- Pre-1979 data from Landsat-3 are not consistent with the post 1979 data.
- Landsat-1 and -4 exhibit the maximum inconsistency (16%) in calculating the TOA reflectance.
- Landsat-2 and -3 have increasing response trend supported by statistical tests.

## Results: Band 2

- Landsat-2, -3, and -5 mean TOA reflectance agree within 1%.
- Landsat-1 and -4 again exhibit the maximum inconsistency (17%) in calculating the TOA reflectance.
- Slightly increasing response trend of Landsat-2 is supported by statistical tests.

## Results: Band 3

- Landsat-1, -2, and -5 calibration seems consistent within 1%.
- Landsat-3 and -4 agree in the calculation of TOA reflectance within 2%.
- No trend in any response was supported by statistical tests.

## Results: Band 4

- Landsat-1 through -4 calibration seems consistent within 6%.
- Variability of data within each sensor is comparatively higher because band 4 is susceptible to the water vapor content in the atmosphere.
- No clear trend exists in any sensor.

## Summary of Lifetime Stability/Consistency of MSS sensors

- Data from each MSS sensor indicates better than expected radiometric stability.
- Absolute gains of all 5 MSS sensors exhibit a maximum difference of 17%.

## Cross-calibration

*Cross-calibration is a post launch calibration method where a given satellite sensor is calibrated against another satellite sensor for which the radiometric calibration  is better known, using simultaneous or near simultaneous imaging of a common ground target.*
- Issues:
*Relative Spectral Response (RSR) profiles*
*Spatial Resolution*
*Misregistration*
*Temporal Differences*

## Cross-calibration of L1 MSS to L2 MSS

## Background

- Six pairs of near-coincident scenes from Sonoran desert are selected.
- For better regression, some additional ROIs with different reflectance values were selected.

| Scene Pairs used (6), Total 9 ROIs |  |
| --- | --- |
| LM10410381975150AAA04 | LM20410381975159AAA05 |
| LM10410381976073AAA02 | LM20410381976082AAA01 |
| LM10410381976109AAA02 | LM20410381976100AAA01 |
| LM10410381976109AAA02 | LM20410381976118AAA04 |
| LM10410381976289AAA04 | LM20410381976280AAA03 |
| LM10410381977262AAA04 | LM20410381977274AAA01 |

- Additional ROIs

## RSR Profiles of Landsat-1 and -2

- Landsat-1 to -2 Cross-calibration Results

## Cross-calibration of L2 MSS to L4 MSS

## Background

- The different temporal resolution of Landsat-2 and -4 (18 days vs. 16 days) provided an opportunity to these instruments on November 9, 1982 to acquire *almost simultaneous image data within minutes*.
- Three pairs of scenes selected for this work.

| Pair No. | Scene Identifier | Date and Time 
Acquired (YYYY:DOY
:HH:MM:SS) | WRS Path | WRS Row | WRS Type | Acquisition Quality | Sun Azimuth ( °) | Cloud Cover |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 1 | LM20340371982313AAA03 | 1982:313:16:56:05 | 34 | 37 | 1 | 9 | 149 | 10 |
|  | LM40320371982313AAA03 | 1982:313:17:00:04 | 32 | 37 | 2 | 9 | 150 | 30 |
| 2 | LM20340341982313AAA03 | 1982:313:16:56:00 | 34 | 34 | 1 | 9 | 151 | 10 |
|  | LM40320341982313AAA03 | 1982:313:16:59:05 | 32 | 34 | 2 | 9 | 152 | 40 |
| 3 | LM20340351982313AAA03 | 1982:313:16:55:04 | 34 | 35 | 1 | 9 | 151 | 10 |
|  | LM40320351982313AAA03 | 1982:313:16:59:02 | 32 | 35 | 2 | 9 | 151 | 20 |

*The difference in sun azimuth arises due to a drift in the scene center.*

## An Example Scene Pair

- LM20340351982313AAA03
- 1982:313:16:56:00
- Sun Elevation = 31°
- Sun Azimuth = 151°

- LM40320351982313AAA03
- 1982:313:16:59:05
- Sun Elevation = 32°
- Sun Azimuth = 151°

## Region of Interest

- Since none of these acquisitions are from known invariant sites, defining precisely geolocated ROI is a real challenge.
- Geographical features were used to avoid any misregistration error.

## RSR Profiles of Landsat-2 and -4

## Landsat-2 to -4 Cross-calibration Results 

## Cross-calibration of L3 MSS to L4 MSS

## Background

- The different temporal resolution of Landsat-3 and -4 (18 days vs. 16 days) also provided an opportunity to these instruments to follow ***identical paths on January 20, 1983 within minutes.***
- Two pairs of good scenes are selected from this dataset to cross-compare the responses of Landsat-3 and -4.

*Altogether eight ROIs were defined in the homogeneous areas on the scenes.*

- _LM30430361983020AAA03_
- 1983:020:17:47:04

- _LM40400361983020AAA03_
- 1983:020:17:51:00

- _LM30170401983012AAA03_
- 1983:012:15:20:00

- _LM40160401983012AAA03_
- 1983:012:15:24:00

## RSR Profiles of Landsat-3 and -4

## Landsat-3 to -4 Cross-calibration Results

## Cross-calibration of L4 MSS to L5 MSS

## Background

- Immediately after launch, the Landsat-5 was initially placed in a tandem orbit close to that of Landsat-4.
- The data acquired during this period was almost simultaneous with a difference of few seconds.
- Two pairs of good scenes were selected from this dataset to cross-compare the responses of Landsat-4 and -5.

*Initially five precisely geolocated ROIs were defined on the scenes.*

- _LM40200181984075XXX03_
- 1984:075:15:38:04

- _LM50200181984075AAA03_
- 1984:075:15:38:02

- _LM40200361984075AAA04_
- 1984:075:15:45:05

- _LM50200361984075AAA03_
- 1984:075:15:45:03

## RSR Profiles of Landsat-4 and -5

## Landsat-4 to -5 Cross-calibration Results

## Validation of Cross-calibration Results

## Methodology

- Sonoran desert site is selected again for validation of cross-cal results.
- Following assumptions are made:
- The Sonoran desert site is stable from 1972 to 1992.
- Any genuine trend observed in the instrument response to this site is the characteristics of the instrument itself.
- Landsat-1 through -4 MSS data from Sonoran desert were transformed to apparent Landsat-5 data using the cross-calibration connections established in the previous part of this presentation.
- Time factor was introduced in the cross-calibration results of Landsat-2 band 1 and 2, and Landsat-3 band 1 to account for the trends they showed in their lifetime responses to Sonora.
- Pre-1979 data from Landsat-3 are left unaltered.

## Results: Band 1

- Before Cross-
- calibration applied

- After Cross-
- calibration applied

## Results: Band 2

- Before Cross-
- calibration applied

- After Cross-
- calibration applied

## Results: Band 3

- Before Cross-
- calibration applied

- After Cross-
- calibration applied

## Results: Band 4

- Before Cross-
- calibration applied

- After Cross-
- calibration applied

## Cross-calibration validation summary

| Sensor | TOA Reflectance | Normalized to L5 | Normalized to L5 after Cross-cal |
| --- | --- | --- | --- |
| L1 | 0.263 | 1.02 | 0.98 |
| L2 | 0.237 | 0.92 | 0.98 |
| L3 | 0.239 | 0.93 | 1 |
| L4 | 0.227 | 0.88 | 1 |
| L5 | 0.258 | 1 | 1 |

| Sensor | TOA Reflectance | Normalized to L5 | Normalized to L5 after Cross-cal |
| --- | --- | --- | --- |
| L1 | 0.343 | 1.08  | 0.99  |
| L2 | 0.319 | 1.00  | 0.99 |
| L3 | 0.325 | 1.02 | 1.00  |
| L4 | 0.294 | 0.92  | 0.99  |
| L5 | 0.318 | 1.00  | 1.00  |

| Sensor | TOA Reflectance | Normalized to L5 | Normalized to L5 after Cross-cal |
| --- | --- | --- | --- |
| L1 | 0.356 | 1.01  | 0.98  |
| L2 | 0.351 | 1.00  | 0.97  |
| L3 | 0.33 | 0.94  | 0.99  |
| L4 | 0.335 | 0.95  | 0.99  |
| L5 | 0.351 | 1.00  | 1.00  |

| Sensor | TOA Reflectance | Normalized to L5 | Normalized to L5 after Cross-cal |
| --- | --- | --- | --- |
| L1 | 0.314 | 0.90  | 1.06  |
| L2 | 0.324 | 0.93  | 1.01  |
| L3 | 0.327 | 0.94  | 1.02  |
| L4 | 0.334 | 0.96  | 1.05  |
| L5 | 0.348 | 1.00  | 1.00  |

**Band 1**

**Band 2**

**Band 3**

**Band 4**

## Equivalent Landsat-5 MSS TOA Reflectance Conversion Factors for Landsat-1 through -4 MSS 

**Example:** Suppose, a TOA reflectance calculation in band 1 over any specified
- ROI of Landsat-2 scene, LM20410381976118AAA04, is found to be 0.234. The
- Equivalent Landsat-5 TOA is given by,
- 		ρL5 =Gain*ρL2 + Offset + Time dependent term
- 		      =1.0772*0.234–0.0079+0.0009858*(1982.86-1976.32)
- 		      =0.251

## Cross-calibration of Landsat-5 MSS to TM

## Background

- Landsat-5 TM is known to have an absolute radiometric accuracy of 5%.
- Absolute calibration of MSS sensors can be achieved by establishing a cross-calibration between Landsat-5 MSS and TM.
- Major issues:
- Spatial resolution
- RSR Differences

## Key Concern: Dissimilar RSR Profiles

- None of the four bands match closely in their RSR profiles, indicating that the two sensors may produce different results while looking at the same ground target.
- Effect of Spectral Band Difference is scene specific, and we need to know the spectral signature of target as well to find the Spectral Band Adjustment Factors (SBAFs).

| MSS | TM | FOM |
| --- | --- | --- |
| B1 | B2 | 0.635 |
| B2 | B3 | 0.708 |
| B3 | B4 | 0.182 |
| B4 | B4 | 0.328 |

**Spectrally best matching pairs**

## Region of Interest (ROI)

- Twelve pairs of coincident TM and MSS scenes acquired by Landsat-5 over Libya-4 desert were selected to cross-calibrate MSS to TM.
- 1000×800 pixels ROI defined on
- 	MSS scenes (which is equivalent to 1900×2187 TM pixels).

- The dune features in the site were used to geolocate the ROI.

## Spectral Band Adjustment Factor (SBAF) Calculation

- Spectral signature of Libya-4 desert was derived using hyperspectral data acquired by Hyperion sensor on Earth Observer-1.

| MSS and TM matching Bands | Average SBAF from two Hyperion data set (TM/MSS) | Percentage    difference (%) |
| --- | --- | --- |
| MSS B1-TM B2 | 1.050  | 0.62 |
| MSS B2-TM B3 | 0.990  | 0.04 |
| MSS B3-TM B4 | 0.903  | 0.11 |
| MSS B4-TM B4 | 1.310  | 5.44 |

## Results

## SBAF Examples (or how do we perform spectrally dependent cross-cal?)

- SBAF Examples (or how do we perform spectrally dependent cross-cal?)

- * Spectral profiles obtained from the ASTER Spectral Library available at http://speclib.jpl.nasa.gov

## Conclusions

- Cross-calibration of TM4 to TM5 accomplished
- Uncertainties 1-3% in all reflective bands, up to 5% in band 5
- Up to 8% differences with respect to NLAPS-based gains
- The radiometric calibration of each MSS sensor was found stable within 2% in band 1, 3% in bands 2 and 3, and 6% in band 4, throughout the lifetime.
- The absolute gains of five MSS sensors exhibit a maximum difference of 17% as derived from the currently existing radiometrically processed MSS data in the USGS archive.
- Cross-calibration connections established so far shows the ability to place Landsat-1 through -5 MSS sensors on a consistent radiometric scale within 6%.
- Initial cross-calibration to Landsat-5 TM using a desert site suggests the absolute radiometric gain of the Landsat-5 MSS is lower in band 1 by 19%, band 2 by 6%,  band 3 by 2%, and in band 4 by 3%.
- Tables of conversion factors coming soon to a website near you!

## Open Issues

- NLAPS calibration of L4 TM and MSS
- Should be ‘easily’ invertible for L4 TM
- MSS radiometric processing not well understood; indications that perhaps only solar zenith angle correction applied.
- LPGS/IAS capability for L4 TM imminent; ***need to insure development of similar capability for MSS***
- Development of spectral-based cross-calibration technique for TM to MSS ?
- Consider atmospheric modeling and BRDF effect.
- Determine the effect of RSR mismatch; particularly for Landsat-2 to -4 and Landsat-3 to -4 cross-calibration.

**Notes:**
Put some graphic on the final slide that looks good.  Maybe a cross-cal example???