# Presentation: 516392

## Study of Sensor Inter-calibrationUsing CLARREO Jack Xiong, Jim Butler, and Steve Platnick NASA/GSFC, Greenbelt, MD 20771 with contributions fromMODIS Characterization Support Team (MCST), NASA/GSFC

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**Study of Sensor Inter-calibration****Using CLARREO**** ***Jack Xiong**, **Jim Butler, and Steve Platnick** **NASA/GSFC, Greenbelt, MD 20771** **with contributions from**MODIS Characterization Support Team (MCST), NASA/GSFC*

***CLARREO Workshop, 21-23 October 2008, Washington, DC***

## Outline

- Introduction
- Applications of CLARREO
- Requirements for CLARREO Observations
- Inter-calibration Approaches Using CLARREO
- Lunar observations
- VIS/NIR/SWIR only
- Simultaneous nadir observations (SNO)
**Ground observations (Dome C)**
**Inter-comparison of Terra and Aqua MODIS calibration**
- Sensitivity Study (future work)
- RSR sensitivity study (using Schiamachy with LaRC)
**Spectral and spatial sensitivity studies of Earth view targets (Hyperion and AVIRIS)**
- Summary

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## Introduction

**Introduction**

**Applications of CLARREO**
**Benchmark Observations**
**Accurate, stable, SI traceable, spectrally resolved **
**Inter-calibration for Other Sensors**
**Consistent data records for long-term climate change**
**Requirements for CLARREO Observations**
**General Requirements**
**Spectral; spatial; temporal; orbital**
**Special Requirements **
**Maneuver (pointing) capability**
**Lunar observations**

## Inter-calibration Approaches Using CLARREO

**Lunar observations**
**MODIS (T/A), SeaWiFS, Hyperion, VIRS/TRMM**
**Simultaneous nadir observations (SNO)**
**MODIS (T/A), AVHRR, AIRS, MISR, ASTR, Landsat, GLI, VIRS/TRMM**
**Ground observations**
**Dome Concordia, Antarctica**
**MODIS (T/A), AVHRR, AIRS, MISR, ASTR**
**Inter-calibration of Terra and Aqua MODIS**

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**Collaboration with USGS (Moon), NOAA, JPL, JAXA, USGC (SNO/Dome C)**

## Inter-calibration Using Lunar Observations

**Inter-calibration Using Lunar Observations**

***MODIS Lunar Observations:***
***via spacecraft maneuvers***
***at fixed phase angle ***
***reference to a lunar model (USGS)***
***using integrated irradiance***

**Images form Aqua MODIS (band 1) Lunar Observations (Oct 04 – Jun 05) **

**Advantages vs disadvantages:**

## Inter-calibration Using SNO

**Inter-calibration Using SNO**

**Terra MODIS**

**Aqua MODIS**

**AVHRR**

**SNO**

**SNO**

***For RSB***

***For TEB***

**Advantages vs disadvantages:**

## Inter-calibration Using a Ground Target

**Aqua MODIS SD Degradation (0.41 to 0.94********m)**
**Any Impact on Calibration?**

**Inter-calibration Using a Ground Target**

**Why using a ground target**
- Validate on-board calibration; complement other cal/val approaches
- Monitor calibration long-term stability
- Support sensor inter-calibration
**Requirements for a ground “calibration” target**
- Spectral and spatial uniformity and radiometric stability (minimum environmental impact)
- Site accessibility and data availability
- Ground measurements of radiometric traceability

## Examples of Using Dome C for Inter-calibration

- Site Description
- Data Selection
- Methodology
- Thermal emissive: reference to Automated Weather Station (AWS) measurements
- Solar reflective: BRDF model based on ground measurements over Antarctic snow
- Results from MODIS
- Recent presentation at SPIE Europe Remote Sensing (Xiong et al. 2008)
- Future Work

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## Site Description

**Site Description**

- Dome Concordia
- Antarctica

- Located on Antarctic Plateau (75.1 S, 123.4 E)
- One of the most homogeneous land surfaces on earth in terms of surface temperature and emissivity.
- Uniformity over spatial scales typical of the ground footprint of satellite sensors
- High altitude (~3200 m) & minimal slope
- Low snow accumulation rate
- Extremely dry, cold & rarefied atmosphere
- Low fractional cloud coverage
- Low atmospheric aerosol and water vapor content
- Permanently manned Research Station now operational
- AWS data available since 1995
- 10-minute averages of meteorological parameters (T, RH, WS, WD, P)
- Daily radiosonde measurements
- Frequent satellite overpass

- CEOS Endorsed Site
- NASA/NOAA/ESA Effort

## Data Selection

**Data Selection**

- MODIS Collection 5 Level 1B data
- Multiple MODIS observations each day (~8) at different angles of incidence.
- Only near-nadir overpasses used (nadir track within +/- 50 km of Dome C). One granule every 2-3 days.
- 20x20 pixel average centered on Dome C
- No cloud screening applied for TEB. All granules used.
- Uniformity screening applied for RSB to eliminate any granules showing greater than 2% non-uniformity in reflectance over the 20x20 pixel area

## Methodology and Approach (TEB)

**Methodology and Approach (TEB)**

**AWS surface temperature measurements are used as a proxy to track any trends in the relative bias between MODIS Terra & Aqua.**
**	****	********T****MODIS**** = BT****MODIS**** – T****AWS****	****	**
**	****	****Relative Bias = ********T****Terra**** – ********T****Aqua****	**
**Relative Bias calculated for each MODIS band and only for days with measurements from both Terra & Aqua.**
**Applications to other sensors: relative spectral response (RSR), spatial resolution (ground footprint)**
**	**

## Methodology and Approach (RSB)

**Methodology and Approach (RSB)**

**A BRDF model developed by Warren et al. (JGR 1998) based on near-surface reflectance measurements over the Antarctic snow**
**      *****R***** (*****θ*****,*****ψ*****,*****φ*****) = *****c*****1**** + *****c*****2*****cos*****(*****π*****- *****φ*****)+ *****c*****3*****cos*****[2(*****π*****- *****φ*****)]**
**	**
**      *****c*****1****, *****c*****2**** and *****c*****3***** *****are functions of *****cos*****(*****θ*****)***** and cos*****(*****ψ*****)**
**      *****c*****1**** = *****a*****0**** + *****a*****1****[1 - *****cos*****(*****ψ*****)], *****c*****2 ****= *****a*****2****[1 - *****cos*****(*****ψ*****)], *****c*****3**** = *****a*****3****[1 - *****cos*****(*****ψ*****)]**
***      ******a*****i**** = *****b*****0i**** + *****b*****1i**** *****cos*****(*****θ*****)***** + b*****2i**** *****cos*****2****(*****θ*****) ***** *****(i***** = *****0, 1, and 2)**
**where *****θ***** is the incident solar zenith angle, *****ψ***** is the viewing zenith angle, and *****φ***** is the relative azimuth angle.**
**A ratio of the observed reflectance factor *****r***** to modeled reflectance factor *****R***** is calculated by**** ****Δ*****r***** = *****r *****/ *****R*****	**
**Spectral BRDF of Antarctic snow from Hudson, Warren et al (JGR 2006) **

## Sensor (11 and 12 m) and AWS Observations

**Sensor (11 and 12 ********m) and AWS Observations**

**Good correlation between sensor and AWS observations**
**(focusing long-term behavior, not individual observations)**

## Relative Bias = TTerra – TAqua  (time)

**Long-term draft (<10mK) for bands 31 and 32; high quality on-board TEB calibration **

**Excellent calibration consistency (11********m: 0.025±2.984K; 12********m: 0.013±3.010K)**

**No obvious temperature dependent bias (<20mK)**

**Relative Bias = ********T****Terra**** – ********T****Aqua  ****(time)**

******T****MODIS**** = BT****MODIS**** – T****AWS**

**Terra: Black diamonds; ****Aqua: Blue squares**

**11********m**

**12********m**

**Relative Bias = ********T****Terra**** – ********T****Aqua ****(temperature)**

## Inter-comparison of Aqua MODIS and AIRS at 11 m

**One orbit – June 20, 2006**
**(near nadir footprints)**

**Dome C data (near nadir)**

**190K – 330K**

**Inter-comparison of Aqua MODIS and AIRS at 11 ********m**
**(using Dome C observations)**

**Old version**
**New version**

## Sensor (0.65 and 0.86 m) Observations

**Sensor (0.65 and 0.86 ********m) Observations**

**strong correlation between sensor observations and solar zenith angle**

## Sensor (0.65 and 0.86 m) Observations versus Modeled Values

**Sensor (0.65 and 0.86 ********m) Observations versus Modeled Values**

**Averaged fitting residual: 1.3 – 1.9% **

**Model parameters derived using sensor first-year observations**

## Terra MODIS observations (0.65m) over Dome C (2002 - 2003)

- Terra MODIS observations (0.65m) over Dome C (2002 - 2003)

## Terra MODIS observations (0.86m) over Dome C (2002 - 2003)

- Terra MODIS observations (0.86m) over Dome C (2002 - 2003)

## Terra and Aqua MODIS observations over Dome C

## Sensitivity Study (future work)

**RSR Sensitivity Study**
**Extend from our previous study reported at April/May CLARREO workshop (e.g., preferred inter-calibration scene types vs. spectral band)**
**Work with LaRC using Schiamachy data**** **
**Spectral and Spatial Sensitivity Studies**
**Hyperion observations, Dome C and other targets**
**0.4 to 2.5********m, 30m IFOV (@705km altitude)**
**AVIRIS observations**
**0.4 to 2.5********m, 1 mrad IFOV**

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## http://eo1.usgs.gov/hyperion.php

**http://eo1.usgs.gov/hyperion.php**

## http://aviris.jpl.nasa.gov/html/aviris.instrument.html

**http://aviris.jpl.nasa.gov/html/aviris.instrument.html**

## Summary

**Summary**

- Sensor Inter-calibration Using CLARREO
- Improve current sensor inter-calibration approaches with highly accurate, stable, and spectrally resolved observations
- Resolve calibration differences or establish calibration consistency among sensors with on-orbit SI traceable measurements
- Ground Target Characterization Using CLARREO
- Extend consistent data records, using observations from previous, current, and future missions/sensors, for studies of long-term climate changes
- Dome C site can be used to track sensor long-term stability and calibration consistency among sensors (challenges in VIS/NIR/SWIW)
- Other Approaches
- Lunar observations; SNO