IRIS Mariner 9 data revisited: 1. An instrumental effect

Small spurious features are present in data from the Mariner 9 Infrared Int erferometer Spectrometer (IRIS). These represent a low amplitude replicatio n of the spectrum with a doubled wavenumber scale. This replication arises principally from an internal reflection of the interferogram at the input w indow. An algorithm is provided to correct for the effect, which is at the 2% level. We believe that the small error in the uncorrected spectra does n ot materially affect previous results; however, it may be significant for s ome future studies at short wavelengths. The IRIS spectra are also affected by a coding error in the original calibration that results in only positiv e radiances. This reduces the effectiveness of averaging spectra to improve the signal to noise ratio at small signal levels. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.