Airborne intercomparison of vacuum ultraviolet fluorescence and tunable diode laser absorption measurements of tropospheric carbon monoxide

During the fall 1997 North Atlantic Regional Experiment (NARE 97), two separate intercomparisons of aircraft-based carbon monoxide measurement instrumentation were conducted. On September 2, CO measurements were simultaneously made aboard the National Oceanic and Atmospheric Administration (NOAA) WP-3 by vacuum ultraviolet (VUV) fluorescence and by tunable diode laser absorption spectroscopy (TDLAS), On September 18, an intercomparison flight was conducted between two separate instruments, both employing the VUV fluorescence method, on the NOAA WP-3 and the U,K. Meteorological Office C-130 Hercules. The results indicate that both of the VUV fluorescence instruments and the TDLAS system are capable of measuring ambient CO accurately and precisely with no apparent interferences in 5 s. The accuracy of the measurements, based upon three independent calibration systems, is indicated by the agreement to within 11% with systematic offsets of less than 1 ppbv. In addition, one of the groups participated in the Measurement of Air Pollution From Satellite (MAPS) intercomparison [Novelli ef at., 1998] with a different measurement technique but very similar calibration system, and agreed with the accepted analysis to within 5%. The precision of the measurements is indicated by the variability of the ratio of simultaneous measurements from the separate instruments, This variability is consistent with the estimated precisions of 1.5 ppbv and 2.2 ppbv for the 5 s average results of the C-130 and the WP-3 instruments, respectively, and indicates a precision of approximately 3.6% for the TDLAS instrument. The excellent agreement of the instruments in both intercomparisons demonstrates that significant interferences in the measurements are absent in air masses that ranged from 7 km in the midtroposphere to boundary layer conditions including subtropical marine air and continental outflow with embedded urban plumes. The intercomparison of the two VUV instruments that differed widely in their design indicates that the VUV fluorescence technique for CO measurements is not particularly sensitive to the details of its implementation. These intercomparisons help to establish the reliability of ambient CO measurements by the VUV fluorescence technique

Mesoscale covariance of transport and CO2 fluxes: Evidence from observations and simulations using the WRF-VPRM coupled atmosphere-biosphere model

We developed a modeling system which combines a mesoscale meteorological model, the Weather Research and Forecasting (WRF) model, with a diagnostic biospheric model, the Vegetation Photosynthesis and Respiration (VPRM). The WRF-VPRM modeling system was designed to realistically simulate high-resolution atmospheric CO₂ concentration fields. In the system, WRF takes into account anthropogenic and biospheric CO₂ fluxes and realistic initial and boundary conditions for CO₂ from a global model. The system uses several “tagged” tracers for CO₂ fields from different sources. VPRM uses meteorological fields from WRF and high-resolution satellite indices to simulate biospheric CO₂ fluxes with realistic spatiotemporal patterns. Here we present results from the application of the model for interpretation of measurements made within the CarboEurope Regional Experiment Strategy (CERES). Simulated fields of meteorological variables and CO₂ were compared against ground-based and airborne observations. In particular, the characterization by aircraft measurements turned out to be crucial for the model evaluation. The comparison revealed that the model is able to capture the main observed features in the CO₂ distribution reasonably well. The simulations showed that daytime CO₂ measurements made at coastal stations can be strongly affected by land breeze and subsequent sea breeze transport of CO₂ respired from the vegetation during the previous night, which can lead to wrong estimates when such data are used in inverse studies. The results also show that WRF-VPRM is an effective modeling tool for addressing the near-field variability of CO₂ fluxes and concentrations for observing stations around the globe

Regional carbon fluxes and the effect of topography on the variability of atmospheric CO2.

Using a mesoscale atmospheric circulation model, it is shown that relatively modest topography height differences of ∼500 m over 200 km near Zotino (60°N, 89°E) in central Siberia may generate horizontal gradients in CO<inf>2</inf> concentration in the order of 30 ppm. In a case study for 15 and 16 July 1996, when Lloyd et al. (2001) conducted a convective boundary layer budget experiment in the area, we show that advection of these gradients disturbs the relation between diurnal concentration changes in the boundary layer and the surface fluxes. This demonstrates that mesoscale atmospheric heterogeneity may have severe impact on the applicability of methods to derive the regional-scale fluxes from CO<inf>2</inf> concentrations measurements, such as the convective boundary layer budget method or inverse modeling. It is shown that similar mesoscale gradients are likely to occur at many long-term observation stations and tall towers. We use the modeled concentration fields to quantify the horizontal and vertical variability of carbon dioxide in the atmosphere. In future observation campaigns, mesoscale processes may be best accounted for by measuring horizontal variability over a few hundred kilometers and by attempting to quantify the representation errors as a function of mesoscale conditions. Copyright 2007 by the American Geophysical Union

Ultrasound navigated RFA of liver tumors

Primary liver tumors and liver metastases are of high clinical relevance. They are the fifth most common kind of malignant tumors and the third most common cause of death in the group of malignant tumors. Ultrasound controlled Radio Frequency Ablation (RFA) is accepted as a gentle and inexpensive treatment but suffers from higher recurrence of tumors compared to surgical resection. The main reasons are that only ultrasound images are available during the intervention and radiological data can not be mapped onto the patient. Therefore, exact positioning of the applicator and control of ablation are very difficult to perform. Thus, RFA as therapy usually is chosen only in cases where surgical resection is not possible. As a part of the BMBF project "FUSION" we are developing a 3D ultrasound based navigation system and aim to improve the interventional process to achieve better outcome for patients who are treated with transcutane, ultrasound controlled RFA. The navigation system provides assistance by mapping radiological information (image sets as well as annotations) onto the patient. During an iterative process 3D ultrasound data can be acquired and target positions as well as trajectories of applicator positions can be planned. Ultrasound probe and applicator needle are navigated continuously and independently. Intuitive navigation scenes enable the physician to gain more orientation and confidence during the different steps of applicator positioning. The incorporation of 3D ultrasound fulfills different purposes: On the one hand, intrainterventional 3D data can be used to improve the registration process, on the other hand they can support the pre- and postinterventional comparison of treated tumors

Iterative navigated resection of malignant glioma by intraoperative 3D-ultrasound

Purpose: Gliomas demonstrate usually a wide variety in echogenicity and the tumour border is not clearly delineated in intraoperative ultrasound. The aim of the study was the development of iterative resection of malignant glioma based on navigated intraoperative 3D-ultrasound. Methods: Six of 30 ultrasound patients were previously selected. For navigation support a freehand 3D ultrasound workstation was used consisting of a standard personal computer containing a video grabber card in combination with an optical tracking system (NDI Polaris) and a standard ultrasound device (Siemens Omnia) with a 7.5 MHz probe. Preoperative 3D-MRI-Dicom data were acquired with a 1.5T Siemens Scanner. All patients underwent early postoperative 3D-MRI. 3D-ultrasound datasets were acquired after craniotomy (transdural), at different subsequent times of the resection procedure and at the end of the operation as well. Unclear tumour borders were analysed by biopsy. Results: All patients suffered on a glioblastoma multiforme (WHO IV). Iterative visualisation of tumour borders was possible during tumour resection in all cases. Pointer based or tracked microscope based navigation was used to identify unclear hyperechoic tissue at the border of the resection cavity. All of these targets could be identified by additional 3D-ultrasound datasets too and were researched by biopsy