# Presentation: 295215

## RSG Vicarious Calibration Results and Automated Approach

- Jeffrey Czapla-Myers
- Remote Sensing Group ~ Optical Sciences Center
- University of Arizona
- Presented at
- MODIS Science Team Meeting
- Baltimore MD
- 22 Mar 2005

## Topics

- Recent reflectance-based results for MODIS
- Summer 2004 field campaign
- Radiance calibration of MODIS and MISR
- MODIS/ASTER cross calibration
- Automated approach to ground-based vicarious calibration using LED radiometers
- Future work

## RSG Field Campaigns at Railroad Valley, NV

- Successful collection
- _2004_
- 2 Jul (A)
- 4 Jul (A)
- 9 Jul (A)
- 10 Jul (T)
- 11 Jul (A)
- 26 Sep (T)
- 13 Dec (T) +
- 15 Dec (T) +
- _2005_
- 12 Mar (T)
- 13 Mar (A)
- 14 Mar (T)
- 15 Mar (A)

- Unsuccessful collection due to bad weather or site inaccessibility
- _2004_
- 6 Jul (T)
- 8 Jul (T)
- 9 Aug (T)
- 18 Sep (A)
- 22 Oct (A)
- 24 Oct (A)
- 26 Oct (T)
- 13 Nov (T)
- 9 Dec (A)
- _2005_
- 10 Jan (A)
- 16 Jan (T)
- 17 Feb (T)
- 5 Mar (T)

## Updated MODIS Results

- 905-nm water vapor

## Updated MODIS Results

## 2004 Summer Campaign

- Railroad Valley Marriott Hotel

- June-July dates were part of larger effort to understand equipment and playa
- RSG’s mobile lab was in Nevada from 14 June to 11 July
- Four Aqua MODIS and one Terra MODIS data collections

## Field Measurements: Summer 2004

- Surface reflectance measurements at Ivanpah Playa, CA
- Measure radiance from playa using transfer radiometer, and well-calibrated reference panel
- Ratio these values to get surface reflectance
- Compare to ASD measurements
- Most bands agree very well except 666 nm
- Surface-leaving radiance at Ivanpah Playa, CA
- Measure radiance with transfer radiometer just above ground
- Compare to radiance calculated using radiative transfer code
- Compare computed vs. measured band-averaged radiance
- 163.69 vs. 162.96 W m-2 sr-1, difference of 0.45% at 666 nm
- MODIS/MISR radiance comparisons of Railroad Valley, NV
- Six dates between Jun & Dec 2004
- Average percent difference between MODIS and MISR bands:
- Blue: 1.5%
- Green: 0.6%
- Red: 1.1%
- NIR: 0.2%

- VNIR transfer radiometer

- ASD studies

## ASTER Cross Calibration Using MODIS

-  Using MODIS to understand other sensors on Terra
-  Sensor geometries are equal
-  Viewing through same atmosphere
-  Surface reflectance the same for nadir view

## Comparison of MODIS with MISR and ASTER

- ASTER dates are after Aug 2002
- MISR and MODIS results use the same nine dates

## Methodology for Automated Ground-Based Vicarious Calibration

- Would like fill in the gaps when we are not at test sites
- MODIS and Landsat 7 ETM+ are always on
- Would like additional points for trend line clarification
- Bad weather and equipment malfunction can limit data collection
- Based on the reflectance-based approach
- Requires different instruments to do the job without personnel
- ASD → LED 			(surface reflectance)
- ASR → Cimel sun photometer 	(atmospheric conditions)
- Elements that need to be accounted for:
- Surface reflectance of test sites
- Climate conditions
- Sky radiance

- ASTER band 1

## LED Radiometers

- Have been used before (e.g. GLOBE project)
- Critical element needed to measure surface reflectance
- Basically an LED used in reverse
- Readily available, inexpensive, robust, and built-in spectral selection
- Three bands: 522, 612, 837 nm
- Laboratory calibration
- Spectral responsivity
- Temperature stability
- Field of view
- Five LED radiometers currently deployed at Railroad Valley
- Four on MODIS site
- One on corner of Landsat/ASTER sites

## Deployment at Railroad Valley

## AERONET

- Provides:
- Atmospheric optical depth
- Aerosol size distribution
- Columnar water vapour
- Retrieved data used in RTC

## Preliminary Results: 18 Mar 2004 & 13 Dec 2004

## 13 Dec 2004 ~ Railroad Valley

## Results

## Concerns

- Spectral calibration: required for each LED?
- Temperature-dependent spectral responsivity
- Quality control from batch to batch?
- Same as Si detectors?
- Will we have to measure each batch for responsivity vs. temperature? Not sure...
- Number of LEDs required on site?
- Must account for spatial variations
- Use of high-resolution imagery to determine locations of LED radiometers

## Next Stage

- Process more MODIS data
- Six dates in 2004
- Four dates in 2005
- In the lab:
- Build and test more LED radiometers
- Test spectral responsivity of LEDs with varying temperature
- Data reduction
- Integrate AERONET data
- Compare results to those reported by MODIS