The needles of a Telegraph machine were provided with metal stops that enabled the Signalmen to hear the message, rather that having to see the message on the indicating needles
A special kind of radiometer which measures changes of atmospheric temperature and changes in water vapor content of the air at various heights in the atmosphere
As applied to GOES satellites: a 19-channel instrument designed to provide visible and infrared spectral radiances, used to vertically probe, or sound, the atmosphere This is done by employing spectral bands with different amounts of atmospheric absorption, in order to measure temperatures and moisture at different depths in the atmosphere Sounder data is typically available from GOES every hour, over the same locations
A special kind of radiometer that measures changes in atmospheric temperature with height, as well as the content of various chemical species in the atmosphere at various levels The High Resolution Infrared Radiation Sounder (HIRS), found on NOAA polar-orbiting satellites, is a passive instrument See passive system