For a prediction of the rate of climate change during the 21st century, there is an urgent need to better understand the global carbon cycle, in particular the processes that control the carbon flows between the various reservoirs, and their interactions with the climate system. Atmospheric carbon dioxide (CO2) represents the main atmospheric phase of this biogeochemical cycle. Due to human activities, the concentration of this most important of the Earth’s greenhouse gases has grown from a pre-industrial average atmospheric mole fraction of about 280 parts per million volume (ppm) to 390.5 ppm in 2011 which is an increase of 40%. CO2 contributes to ~63% to the overall global radiative forcing.
Carbon dioxide (CO2) and methane (CH4) are the most important of the greenhouse gases that are directly influenced by
human activities. The Integrated Path Differential Absorption (IPDA) lidar technique using hard target reflection in the
near IR (1.57μm and 1.64μm) to measure the column-averaged dry air mixing ratio of CO2 and CH4 with high precision
and low bias has the potential to deliver measurements from space and air that are needed to understand the sources and
sinks of these greenhouse gases. CO2 and CH4 IPDA require tunable laser sources at 1.57 μm and 1.64 μm that coincide
with appropriate absorption lines of these species having high pulse energy and average power as well as excellent
spectral and spatial properties.
Within this study we have realized more than 50mJ of pulse energy in the near IR coincident with appropriate absorption
lines using an injection-seeded optical parametric oscillator-amplifier system pumped at 100 Hz. At the same time this
device showed excellent spectral and spatial properties. Bandwidths of less than 100 MHz with a high degree of spectral
purity (> 99.9 %) have been achieved. The frequency stability was likewise excellent. The M2-factor was better than 2.3.
Owing to these outstanding properties optical parametric devices are currently under investigation for the CH4 lidar
instrument on the projected French-German climate satellite MERLIN. A similar device is under development at DLR
for the lidar demonstrator CHARM-F which will enable the simultaneous measurement of CO2 and CH4 from an
airborne platform.
Tropospheric profiles of water vapour and wind were measured with differential absorption lidar (DIAL) and heterodyne
detection wind lidar collocated onboard the DLR Falcon research aircraft during the Convective and Orographicallyinduced
Precipitation Study (COPS; www.cops2007.de) over Southwest Germany in summer 2007. This international
field campaign aimed at refining observational and modelling efforts to improve the forecast skill of convective
precipitation over complex terrain in the summer season. The DIAL, a completely new system with four wavelengths
(each 50 Hz, 40 mJ) at 935 nm, was installed nadir-viewing. The 2-micron wind lidar was operated either in scanning
mode at 20 degrees off-nadir for 3d-wind profiles or in nadir-viewing mode for high resolution vertical wind
measurements. The unique combination of both lidars enables the measurement of both horizontal (humidity advection)
and vertical (latent heat) fluxes of water vapour that play an eminent role in precipitation forecast and convection
initiation. The wind lidar's spatial resolution is 100 m in the vertical and 150 m (vertical wind, boundary layer) to 12 km
(3d-wind profiles, whole troposphere) in the horizontal. The DIAL horizontal and vertical resolution ranges from 150 m
in the boundary layer to 500 m in the upper troposphere. This high spatial resolution permits the investigation of smallscale
processes such as turbulent humidity transport in the convective boundary layer or orographically-induced flow
perturbations. Likewise, meso- and synoptic scale processes, e.g. upper level potential vorticity streamers were sampled
by flying extended legs across Western Europe.
Trace gases are components of the Earth's atmosphere influencing weather and climate significantly. They play an important role in atmosphere's chemistry. Ground-based and airborne Differential-Absorption-Lidar-Systems (DIAL) designed for atmospheric investigations are operated since 20 years. Based on the long-term experience in development and operation, the DLR Lidar group initiated a new airborne water vapour Lidar experiment which will perform its first test flight in 2006. Software simulation is one of the major tools for the development of such complex opto-electronic systems. It allows the optimization of system parameters and observation conditions, the development and test of data processing software and the estimation of the capabilities of the sensor system in terms of product quality. The paper describes the physical basics and the DLR DIAL concept. The simulations' end results are presented.
We present measurements of water vapor using a differential absorption lidar (DIAL) system mounted downward looking on board a meteorological research aircraft. Flight tracks flown in 1.5 - 3 km above ground show the height and entrainment structure of the atmospheric boundary layer top. Cross sections of water vapor can be used to study for example land- sea interactions or the structure of thermals in a convective boundary layer. Applying spectral and autocorrelation analyses across horizontal DIAL water vapor series gives insight into the turbulent structure of the atmosphere. Vertical fluxes of humidity at the top of the boundary layer can be estimated from the DIAL variance water vapor profiles using a set of empirically derived equations. Such measurements are of high climatological interest, since they enable us to evaluate and monitor evaporation and biosphere-atmosphere exchange processes.
An airborne near infrared differential absorption lidar (DIAL) has been completed for meteorological applications. This system is based on a Nd:YAG pumped narrow-band tunable dye laser for both the on- and off-line measurements. Performing H2O measurements within and above the planetary boundary layer (PBL) up to an altitude of 4 km, it successfully participated in the European Field Experiment on Desertification Threatened Areas (EFEDA '91) conducted in Spain in the summer of 1991. Data processing of the lidar signals provides range resolved horizontal and vertical water vapor profiles, horizontal power spectra of turbulence, and aerosol backscattering profiles. Water vapor profiles are being calculated using gliding averages of single lidar returns. Typical horizontal resolutions range from 1.3 to 3 km with vertical resolutions varying from 300 to 600 m, depending on the signal-to-noise ratio, in order to meet a 5 to 10% accuracy. The systematic errors, however, are estimated to be around 6%. The vertical water vapor profiles agree well with radiosonde measurements.
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