Dietrich G. Feist

A new 22-GHz radiometer for middle atmospheric water vapor profile measurements

We report on the Middle Atmospheric Water Vapor Radiometer (MIAWARA) instrument, a new ground-based 22-GHz-radiometer that provides water vapor profiles with an altitude coverage of 22-80 km. This paper focuses on the instrumentation and calibration of the new instrument. It is a noncooled instrument with a very low receiver noise temperature, even lower than receiver noise temperatures of existing cooled instruments. The calibration of MIAWARA is achieved with so-called tipping-curve and balanced calibration schemes. The combination of these two calibration techniques allows us to set up a different calibration scheme than most of the other, rarely existing, water vapor profile radiometers at 22 GHz without the commonly used liquid nitrogen calibration. With the use of tipping-curve calibrations, the instrument operates as a standalone instrument. This independence of liquid-nitrogen-cooled calibration targets and of other instruments makes MIAWARA a suitable instrument for campaign use. In addition to the instrumental and calibrational description, a validation technique for the tipping-curve calibration is presented. Finally, first results obtained by measurements carried out in the Swiss plateau are reported.

Middle Atmospheric Water Vapour Radiometer (MIAWARA): Validation and first results of the LAPBIAT Upper Tropospheric Lower Stratospheric Water Vapour Validation Project (LAUTLOS‐WAVVAP) campaign

[1] We present a validation study for the ground-based Middle Atmospheric Water Vapour Radiometer (MIAWARA) operating at 22 GHz. MIAWARA measures the water vapor profile in the range of 20–80 km. The validation was conducted in two phases at different geographical locations. During the first operational period the radiometer was operated at middle latitudes in Bern, Switzerland, and the measured water vapor profiles were compared with the HALOE satellite instrument. The agreement between HALOE and MIAWARA was for most altitudes better than 10%. In the second comparison phase, MIAWARA took part in the Lapland Atmosphere-Biosphere Facility (LAPBIAT) Upper Tropospheric Lower Stratospheric Water Vapour Validation Project (LAUTLOSWAVVAP) campaign in early 2004 in the subarctic region of northern Finland. During this campaign, different balloon sondes probed the water vapor content in the upper troposphere and lower stratosphere. The stratospheric water vapor profiles of the fluorescent hygrometer FLASH-B and the NOAA frost point hygrometer mirror in the range of 20–26 km were compared with the lowermost retrieval points of MIAWARA. The agreement between the balloon instruments and MIAWARA was better than 2% for a total number of 10 comparable flights. This showed the potential of MIAWARA in water vapor retrieval down to 20 km. In addition, the northern Finland MIAWARA profiles were compared with POAM III water vapor profiles. This comparison confirmed the good agreement with the other instruments, and the difference between MIAWARA and POAM was generally less than 8%. Finally, the tipping curve calibration was validated with tipping curve measurements of the All-Sky Multi Wavelength Radiometer (ASMUWARA) which was operated 10 months side by side with MIAWARA. The agreement of the tropospheric opacity derived from these tipping curves agree within 1%.

An Assessment of Pseudo-Operational Ground-Based Light Detection and Ranging Sensors to Determine the Boundary-Layer Structure in the Coastal Atmosphere

Twenty-one cases of boundary-layer structure were retrieved by three co-located remote sensors, One LIDAR and two ceilometers at the coastal site of Mace Head, Ireland. Data were collected during the ICOS field campaign held at the GAW Atmospheric Station of Mace Head, Ireland, from 8th to 28th of June, 2009. The study is a two-step investigation of the BL structure based on (i) the intercomparison of the backscatter profiles from the three laser sensors, namely the Leosphere ALS300 LIDAR, the Vaisala CL31 ceilometer and the Jenoptik CHM15K ceilometer; (ii) and the comparison of the backscatter profiles with twenty-three radiosoundings performed during the period from the 8th to the 15th of June, 2009. The sensor-independent Temporal Height-Tracking algorithm was applied to the backscatter profiles as retrieved by each instrument to determine the decoupled structure of the BL over Mace Head. The LIDAR and ceilometers-retrieved BL heights were compared to the radiosoundings temperature profiles. The comparison between the remote and the in-situ data proved the existence of the inherent link between temperature and aerosol backscatter profiles and opened at future studies focusing on the further assessment of LIDAR-ceilometer comparison.

Correction scheme for close-range lidar returns

Because of the effect of defocusing and incomplete overlap between the laser beam and the receiver field of view, elastic lidar systems are unable to fully capture the close-range backscatter signal. Here we propose a method to empirically estimate and correct such effects, allowing to retrieve the lidar signal in the region of incomplete overlap. The technique is straightforward to implement. It produces an optimized numerical correction by the use of a simple geometrical model of the optical apparatus and the analysis of two lidar acquisitions taken at different elevation angles. Examples of synthetic and experimental data are shown to demonstrate the validity of the technique.

An airborne radiometer for stratospheric water vapor measurements at 183 GHz

The Airborne Millimeter- and Submillimeter Observing System (AMSOS) is a total-power radiometer for observations of the 183.3-GHz water vapor rotational line, operated onboard a Learjet aircraft of the Swiss Air Force. The radiometer is also used to observe the 175.45-GHz ozone line in the other sideband. The neatly designed quasi optics provide a regular and narrow output beam with a half-power beam-width angle of 1.2/spl deg/ and efficient sideband switching. A /spl lambda//4-quasi-optical isolator is used for baseline reduction securing attenuation of internal reflections by more than 30 dB. A low noise temperature of the ambient-temperature-operating system (1900 K) and excellent target pointing (better than 0.1/spl deg/) provide a good duty cycle and reliable calibration. A reliable control over the radiometers operational parameters, like system stability and system temperatures, and higher automatization were required to come up with high demands of an onboard operation. The measured spectra look typical for the region and time where they were observed.

First water vapor measurements at 183 GHz from the high alpine station Jungfraujoch

During six months in 1999, we observed the water vapor emission line at 183.31 GHz with a microwave radiometer at the high alpine site Jungfraujoch in Switzerland. We retrieved statistics on the atmospheric transmission and profiles of stratospheric water vapor on selected days. Our site seems well suited for observations of this spectral line.

The Bernese atmospheric multiple catalog access tool (BEAMCAT): a tool for users of popular spectral line catalogs

Abstract Users of spectroscopic data bases in the microwave region quickly realize that each existing spectral line catalog provide only part of the information that they would like to have. As a workaround for this problem, several merged spectral line data bases have been created by different groups. However, these merged data bases are usually very specific for a certain application and are difficult to maintain. The BEAMCAT data base takes a totally new approach that makes it possible to generate merged spectral line catalogs from any number of source catalogs in multiple user-defined formats. The current version of BEAMCAT contains the complete JPL and HITRAN catalog. Other catalogs like GEISA will soon be included, too. As a first application of the BEAMCAT data base, the author conducted a thorough intercomparison of spectral parameters for all the transitions that the JPL catalog and HITRAN have in common. The intercomparison shows that the spectral parameters in the catalogs are by no means identical. While the difference in center frequency is usually small, the differences in line intensity reach from almost exact match to discrepancies of several orders of magnitude. While it cannot be ruled out that some of the lines were matched incorrectly, this intercomparison might be helpful to identify problems with the original catalogs.

Validation of stratospheric ClO measurements from the Millimeter-wave Atmospheric Sounder (MAS)

During three missions in 1992, 1993, and 1994, the Millimeter-wave Atmospheric Sounder (MAS) measured volume mixing ratio profiles of stratospheric chlorine monoxide (ClO) at 204 GHz from the space shuttle. Owing to the space shuttle orbit, measurements were restricted to tropical and midlatitudes. We compared zonal mean profiles to correlative ClO measurements by an airborne 649 GHz radiometer, a ground-based 278 GHz instrument on Mauna Kea, Hawaii, and Version 4 ClO profiles by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS). The agreement between MAS and all the other instruments was well within the combined error bars over a pressure range of 0.4–40 hPa. Further comparisons of MAS and MLS day-night difference profiles produced an agreement of typically better than 0.1 ppbv. A detailed analysis proved that this agreement was independent of the a priori information that was used for the retrieval of the different data sets.

The Orbiting Carbon Observatory (OCO-2) tracks 2-3 peta-gram increase in carbon release to the atmosphere during the 2014-2016 El Niño

The powerful El Niño event of 2015–2016 – the third most intense since the 1950s – has exerted a large impact on the Earth’s natural climate system. The column-averaged CO2 dry-air mole fraction (XCO2) observations from satellites and ground-based networks are analyzed together with in situ observations for the period of September 2014 to October 2016. From the differences between satellite (OCO-2) observations and simulations using an atmospheric chemistry-transport model, we estimate that, relative to the mean annual fluxes for 2014, the most recent El Niño has contributed to an excess CO2 emission from the Earth’s surface (land + ocean) to the atmosphere in the range of 2.4 ± 0.2 PgC (1 Pg = 1015 g) over the period of July 2015 to June 2016. The excess CO2 flux is resulted primarily from reduction in vegetation uptake due to drought, and to a lesser degree from increased biomass burning. It is about the half of the CO2 flux anomaly (range: 4.4–6.7 PgC) estimated for the 1997/1998 El Niño. The annual total sink is estimated to be 3.9 ± 0.2 PgC for the assumed fossil fuel emission of 10.1 PgC. The major uncertainty in attribution arise from error in anthropogenic emission trends, satellite data and atmospheric transport.

Calibration of a 22-GHz radiometer for middle-atmospheric water vapor measurements: a non-common approach

The Institute of Applied Physics has developed a new ground-based radiometer for measurements of water vapour profiles in the stratosphere and mesosphere. The uncooled instrument, called MIAWARA, has a very good sensitivity and is calibrated using a combination of tipping curve and balancing calibration. Using this combination the instrument can operate as a self calibrating system without the need for routine maintenance. We present a validation technique for the tipping curve calibration and a new approach for the reference absorber design used in the balancing calibration. The uncommon design of the reference absorbers decreases standing wave artifacts and thus enhances the sensitivity of the instrument, leading to a very good altitude coverage in the range of 20 - 80 kilometres.