# Presentation: 774973

## The contribution of the SOLCON instrument to the long term Total Solar Irradiance observation

- S. Dewitte, A. Joukoff, D. Crommelynck, RMIB
- R. B. Lee III, NASA LARC
- R. Helizon, JPL

## Overview

- 0. Objective
- 1. The SOLCON type radiometer
- 2. Observations during the IEH-3 mission
- 3. Determination of the VIRGO SARR coefficients
- 4. Verification ageing ERBS radiometer
- 5 SARR solar irradiance
- 6. Conclusions

## 0.	Objective

- long term observation of Total Solar Irradiance, important for global climate change studies
- has to be done from space
- is a challenge due to drifts and limited instrument lifetimes

## 1.	The SOLCON type radiometer

- 2 symmetrical cavities for the measurement of the absorbed solar radiation
- heath flux sensors between cavities and heath sink
- electrical resistances in the cavities for electrical power calibration
- servo system to obtain equilibrium between cavities
- works as “thermal pair of scales”

## Irradiance determination

- simple approximation SI = (Pclosed-Popen)/A
- corrections needed
- thermal emission shutters
- absorption cavity
- efficiency cavity
- diffraction
- ...

## 2. Observations during 	the IEH-3 mission

- flight from 29/10/1998 to7/11/1998
- solar observation during 11 dedicated + 7 non dedicated solar periods
- reduction measured irradiance to 1 A.U. S=SI/rsun-shuttle2 rsun-shuttle = distance earth shuttle in A.U.determined from position earth relative to sun and shuttle relative to earth

## 3.	Determination of the 	VIRGO SARR coefficients

- SARR = ensemble of instrument adjustment coefficients a to relate relate them to common reference
- SARR adjusted SOLCON measurements:aSOLCON-L SSOLCON-L (t), aSOLCON-R SSOLCON-R (t)
- original measurements VIRGO radiometers: SDIARAD-L (t), SPMO-VA (t)
- SARR coefficient = ratio of means

## 3.	Determination of the 	VIRGO SARR coefficients (continued)

- aDIARAD-L = aSOLCON-L/R SSOLCON-L (t)/ SDIARAD-L (t)               = 1.000025 aPMO-VA = aDIARAD-L SDIARAD-L (t)/ SPMO-VA (t)               = 1.000279

## 4.	Verification aging 	ERBS radiometer

- ERBS radiometer = measures solar irradiance since 1985
- SARR adjustment coefficient was defined during ATLAS 2 shuttle flight
- comparison SARR adjusted ERBS and VIRGO measurements provides verification of the ageing between ATLAS 2 (April 1993) and IEH 3 (October/November 1998)

## 4.	Verification aging 	ERBS radiometer (continued)

- aERBS SERBS (t) / aDIARAD-L SDIARAD-L (t) = 0.99993
- aERBS SERBS (t) / aPMO-VA SPMO-VA (t) = 0.99995
- standard deviation ratio = 0.00014
- no significant ageing of ERBS

## 5.	SARR solar irradiance

- available long term measurements
- Nimbus-7 (1978-1992)
- ACRIM I (1980-1989)
- ERBS (1985-...)
- ACRIM II (1991-...)
- SOVA 1 (1992-1993)
- SOVA 2 (1992-1993)
- DIARAD/VIRGO (1996-...)
- PMO/VIRGO (1996-...)

## 5.	SARR solar irradiance (continued)

- SARR adjusted measurement single instrument ainstrument Sinstrument (t)
- SARR solar irradiance = mean of all available SARR adjusted measurements of individual instruments

## 6.	Conclusions

- The SOLCON measurements obtained during the IEH-3 flight were of good quality.
- They allowed the determination of the SARR coefficients for the VIRGO radiometers.
- They indicated that the ERBS radiometer did not age significantly between 1993 and 1998.
- A SARR solar irradiance from 1978 to the present has been obtained.