Between 25-35% of the Earth's outgoing longwave radiation (OLR) lies in the far-infrared (FIR) spec tral region from 0-500cm-1 where the emission is primarily due to water vapour loc ated in the upper and mid troposphere. The loc al maximum in the absorption spec trum of ic e means that high, c old c irrus c louds have a large effec t on intensity of the OLR here. To date, no FIR measurements of the OLR have been made from spac e, resulting in a major gap in our understanding of the Earth's radiative energy budget. Suc h measurements will provide vital information about the spatial and temporal variability of the OLR with relation to upper tropospheric humidity and c louds whic h will better c onstrain radiation parameterisations in general c irc ulation models. REFIR (the Radiation Explorer in the Far-Infrared) is a polarising interferometer designed to bridge this knowledge gap by measuring the OLR from 100-1100c m-1 at a spec tral resolution of 0.5c m-1. This instrument's performanc e is critic ally dependent on the properties (transmittanc e and reflec tanc e) of the wire grid polarisers it uses as beamsplitters. These properties have been measured at Imperial College and inc orporated into a mathematic al (Jones' matrix) model of the interferometer's performanc e to produc e simulated interferograms and spec tra. When c oupled to a model of detec tors suitable for the FIR spec tral region, potential spec tral noise c haracteristic s of the c alibrated radianc e spec tra produc ed by REFIR have been modelled. So far, c ryogenic ally c ooled detec tor systems are far preferable to ambient temperature detec tors, although measurements with un-c ooled devic es with suitable ac c urac ies are possible with longer integration times. The effec ts of the c hanging sc ene beneath the interferometer during the interferogram ac quisition time have been analysed.
Bolton M., Harries J., Palchetti L., Rizzi R., Caldwell M. (2005). The Earth's outgoing longwave radiation spectrum as seen by REFIR. SAN FRANCISCO : SPIE - The International Society for Optical Engin.
The Earth's outgoing longwave radiation spectrum as seen by REFIR
RIZZI, ROLANDO;
2005
Abstract
Between 25-35% of the Earth's outgoing longwave radiation (OLR) lies in the far-infrared (FIR) spec tral region from 0-500cm-1 where the emission is primarily due to water vapour loc ated in the upper and mid troposphere. The loc al maximum in the absorption spec trum of ic e means that high, c old c irrus c louds have a large effec t on intensity of the OLR here. To date, no FIR measurements of the OLR have been made from spac e, resulting in a major gap in our understanding of the Earth's radiative energy budget. Suc h measurements will provide vital information about the spatial and temporal variability of the OLR with relation to upper tropospheric humidity and c louds whic h will better c onstrain radiation parameterisations in general c irc ulation models. REFIR (the Radiation Explorer in the Far-Infrared) is a polarising interferometer designed to bridge this knowledge gap by measuring the OLR from 100-1100c m-1 at a spec tral resolution of 0.5c m-1. This instrument's performanc e is critic ally dependent on the properties (transmittanc e and reflec tanc e) of the wire grid polarisers it uses as beamsplitters. These properties have been measured at Imperial College and inc orporated into a mathematic al (Jones' matrix) model of the interferometer's performanc e to produc e simulated interferograms and spec tra. When c oupled to a model of detec tors suitable for the FIR spec tral region, potential spec tral noise c haracteristic s of the c alibrated radianc e spec tra produc ed by REFIR have been modelled. So far, c ryogenic ally c ooled detec tor systems are far preferable to ambient temperature detec tors, although measurements with un-c ooled devic es with suitable ac c urac ies are possible with longer integration times. The effec ts of the c hanging sc ene beneath the interferometer during the interferogram ac quisition time have been analysed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
