A ground-based spectrometer equipped with an InGaAs array for routine observations of OH(3-1) rotational temperatures in the mesopause region

Abstract

We present a new spectrometer with high temporal resolution for the observation of OH Meinel band emission dynamics in the spectral range between 1.5µm and 1.6µm. The instrument was developed and is now in operation at the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) in Oberpfaffenhofen (11.27°E, 48.08°N), Germany—a measurement station of the international Network for the Detection of Mesosphere Change (NDMC). It is equipped with a thermoelectrically cooled 512 element InGaAs-photodiode array (PDA) and a polychromator with a grating blazed for 1.6µm. During routine operation one spectrum is obtained every 15s, originating from a field of view of approximately 15°×15° corresponding to ~24×24km2 in 87km height, the peak height of the OH emission layer. The covered wavelength range allows the observation of the OH(3-1) Q- and P-branches as well as of the OH(4-2) R- and Q-branches. Rotational temperatures are calculated using OH(3-1) P-branch emissions between 1.52µm and 1.55µm. Being the successor of the older scanning grating spectrometers of the GRIPS type it is named Ground-based Infrared P-branch Spectrometer (GRIPS 6).A fully automated data acquisition and analysis scheme has also been developed, that covers the complete processing chain from data recording to derivation of rotational temperatures and to long-term archiving. For the estimation of a nocturnal mean value all samples of the nightly temperature time series are weighted according to their individual precision. Thus, mean temperatures between 1 and 2K are lower compared to the unweighted arithmetic mean. Data products are archived at the World Data Center for Remote Sensing of the Atmosphere (WDC-RSAT) and results are displayed at the website of the Network for the Detection of Mesosphere Change (NDMC). A summary of the data obtained during the first 40 months of operation at the German Remote Sensing Data Center as well as aspects of data processing efforts are presented.