Double Bright Band Observations with High-Resolution Vertically Pointing Radar, Lidar, and Profiles

On 11 May 2010, an elevated temperature inversion associated with an approaching warm front produced two melting layers simultaneously, which resulted in two distinct bright bands as viewed from the ER-2 Doppler radar system, a vertically pointing, coherent X band radar located in Greenbelt, MD. Due to the high temporal resolution of this radar system, an increase in altitude of the melting layer of approximately 1.2 km in the time span of 4 min was captured. The double bright band feature remained evident for approximately 17 min, until the lower atmosphere warmed enough to dissipate the lower melting layer. This case shows the relatively rapid evolution of freezing levels in response to an advancing warm front over a 2 h time period and the descent of an elevated warm air mass with time. Although observations of double bright bands are somewhat rare, the ability to identify this phenomenon is important for rainfall estimation from spaceborne sensors because algorithms employing the restriction of a radar bright band to a constant height, especially when sampling across frontal systems, will limit the ability to accurately estimate rainfall

Improvement of Raman lidar algorithm for quantifying aerosol extinction

Aerosols are particles of different composition and origin and influence the formation of clouds which are important in atmospheric radiative balance. At the present there is high uncertainty on the effect of aerosols on climate and this is mainly due to the fact that aerosol presence in the atmosphere can be highly variable in space and time. Monitoring of the aerosols in the atmosphere is necessary to better understanding many of these uncertainties. A lidar (an instrument that uses light to detect the extent of atmospheric aerosol loading) can be particularly useful to monitor aerosols in the atmosphere since it is capable to record the scattered intensity as a function of altitude from molecules and aerosols. One lidar method (the Raman lidar) makes use of the different wavelength changes that occur when light interacts with the varying chemistry and structure of atmospheric aerosols. One quantity that is indicative of aerosol presence is the aerosol extinction which quantifies the amount of attenuation (removal of photons), due to scattering, that light undergoes when propagating in the atmosphere. It can be directly measured with a Raman lidar using the wavelength dependence of the received signal. In order to calculate aerosol extinction from Raman scattering data it is necessary to evaluate the rate of change (derivative) of a Raman signal with respect to altitude. Since derivatives are defined for continuous functions, they cannot be performed directly on the experimental data which are not continuous. The most popular technique to find the functional behavior of experimental data is the least-square fit. This procedure allows finding a polynomial function which better approximate the experimental data. The typical approach in the lidar community is to make an a priori assumption about the functional behavior of the data in order to calculate the derivative. It has been shown in previous work that the use of the chi-square technique to determine the most likely functional behavior of the data prior to actually calculating the derivative eliminates the need for making a priori assumptions. We note that the a priori choice of a model itself can lead to larger uncertainties as compared to the method that is validated here. In this manuscript, the chi-square technique that determines the most likely functional behavior is validated through numerical simulation and by application to a large body of Raman lidar measurements. In general, we show that the chi-square approach to evaluate aerosol extinction yields lower extinction uncertainty than the traditional technique. We also use the technique to study the feasibility of developing a general characterization of the extinction uncertainty that could permit the uncertainty in Raman lidar aerosol extinction measurements to be estimated accurately without the use of the chi-square technique

Wind Profiling from a New Compact, Pulsed, 2-Micron, Coherent-Detection Doppler Lidar Transceiver during Wind Measurement Intercomparison

NASA Langley Research Center has a long history of developing 2-micron laser transmitter for wind sensing. With support from NASA Laser Risk Reduction Program (LRRP) and Instrument Incubator Program (IIP), NASA Langley Research Center has developed a state-of-the-art compact lidar transceiver for a pulsed coherent Doppler lidar system for wind measurement. This lidar system was recently deployed at Howard University facility in Beltsville, Maryland, along with other wind lidar systems. Coherent Doppler wind lidar ground-based wind measurements and comparisons with other lidars and other sensors will be presented

Analysis of Raman Lidar and radiosonde measurements from the AWEX-G field campaign and its relation to Aqua validation

Early work within the Aqua validation activity revealed there to be large differences in water vapor measurement accuracy among the various technologies in use for providing validation data. The validation measurements were made at globally distributed sites making it difficult to isolate the sources of the apparent measurement differences among the various sensors, which included both Raman lidar and radiosonde. Because of this, the AIRS Water Vapor Experiment-Ground (AWEX-G) was held in October - November, 2003 with the goal of bringing validation technologies to a common site for intercomparison and resolution of the measurement discrepancies. Using the University of Colorado Cryogenic Frostpoint Hygrometer (CFH) as the water vapor reference, the AWEX-G field campaign resulted in new correction techniques for both Raman lidar, Vaisala RS80-H and RS90/92 measurements that significantly improve the absolute accuracy of those measurement systems particularly in the upper troposphere. Mean comparisons of radiosondes and lidar are performed demonstrating agreement between corrected sensors and the CFH to generally within 5% thereby providing data of sufficient accuracy for Aqua validation purposes. Examples of the use of the correction techniques in radiance and retrieval comparisons are provided and discussed

Compact, High Energy 2-micron Coherent Doppler Wind Lidar Development for NASA's Future 3-D Winds Measurement from Space

This paper presents an overview of 2-micron laser transmitter development at NASA Langley Research Center for coherent-detection lidar profiling of winds. The novel high-energy, 2-micron, Ho:Tm:LuLiF laser technology developed at NASA Langley was employed to study laser technology currently envisioned by NASA for future global coherent Doppler lidar winds measurement. The 250 mJ, 10 Hz laser was designed as an integral part of a compact lidar transceiver developed for future aircraft flight. Ground-based wind profiles made with this transceiver will be presented. NASA Langley is currently funded to build complete Doppler lidar systems using this transceiver for the DC-8 aircraft in autonomous operation. Recently, LaRC 2-micron coherent Doppler wind lidar system was selected to contribute to the NASA Science Mission Directorate (SMD) Earth Science Division (ESD) hurricane field experiment in 2010 titled Genesis and Rapid Intensification Processes (GRIP). The Doppler lidar system will measure vertical profiles of horizontal vector winds from the DC-8 aircraft using NASA Langley s existing 2-micron, pulsed, coherent detection, Doppler wind lidar system that is ready for DC-8 integration. The measurements will typically extend from the DC-8 to the earth s surface. They will be highly accurate in both wind magnitude and direction. Displays of the data will be provided in real time on the DC-8. The pulsed Doppler wind lidar of NASA Langley Research Center is much more powerful than past Doppler lidars. The operating range, accuracy, range resolution, and time resolution will be unprecedented. We expect the data to play a key role, combined with the other sensors, in improving understanding and predictive algorithms for hurricane strength and track.

Water Vapor Measurements by Howard University Raman Lidar during the WAVES 2006 Campaign

Retrieval of water vapor mixing ratio using the Howard University Raman Lidar is presented with emphasis on three aspects: i) performance of the lidar against collocated radiosondes and Raman lidar, ii) investigation of the atmospheric state variables when poor agreement between lidar and radiosondes values occurred and iii) a comparison with satellite-based measurements. The measurements were acquired during the Water Vapor Validation Experiment Sondes/Satellites 2006 field campaign. Ensemble averaging of water vapor mixing ratio data from ten night-time comparisons with Vaisala RS92 radiosondes shows on average an agreement within 10 % up to approx. 8 km. A similar analysis of lidar-to-lidar data of over 700 profiles revealed an agreement to within 20 % over the first 7 km (10 % below 4 km). A grid analysis, defined in the temperature - relative humidity space, was developed to characterize the lidar - radiosonde agreement and quantitatively localizes regions of strong and weak correlations as a function of altitude, temperature or relative humidity. Three main regions of weak correlation emerge: i) regions of low relative humidity and low temperature, ii) moderate relative humidity at low temperatures and iii) low relative humidity at moderate temperatures. Comparison of Atmospheric InfraRed Sounder and Tropospheric Emission Sounder satellites retrievals of moisture with that of Howard University Raman Lidar showed a general agreement in the trend but the formers miss a lot of the details in atmospheric structure due to their low resolution. A relative difference of about 20 % is usually found between lidar and satellites measurements

Optimal Attitude Guidance for the EXACT and IMPRESS Cubesats using Graph Methods with Pruning

This work demonstrates a high-level mission planning method for maximizing data output from a pair of scientific CubeSat missions. The proposed approach identifies the optimal sequence of attitude maneuvers to perform in order to maximize total downlinked data over the mission, while considering constraints on available power. Many scientific satellite missions consist of at least three target attitudes: pointing solar panels towards the Sun for power, pointing an antenna towards a ground station to transmit data, or pointing a payload towards a point of scientific interest. While careful mechanical design of the mission may enable all three (or more) target attitudes to be achieved simultaneously in certain cases, in general a decision must be made about which target to point to at what time in order to optimally achieve mission objectives and satisfy mission constraints. In this work, we develop a mission planning method that maximizes the volume of data downlinked to the ground over the mission time horizon while respecting constraints on battery level. The optimization problem is posed as an integer program over the space of attitude trajectories and subject to battery constraints. The solution of this problem is an attitude sequence that can be used as a reference for a low-level attitude controller to track. Previous work on this problem suffered from slow solution time for complex mission scenarios which constrained the realism of simulations performed for validation, so in this work we build on our prior approach by leveraging more advanced pruning and search methods to improve optimizer efficiency. We demonstrate the proposed approach on two CubeSats: IMPRESS and EXACT, both currently in design and sharing many mechanical specifications. Both CubeSats are controlled by low-bandwidth actuators and have three main attitude targets: the Sun for power, the Crab Nebula or the Sun the scientific mission, and ground stations for communication. Using simulated orbit data, we show the effectiveness of this method in squeezing mission performance out of both CubeSats while maintaining on-board power. Additionally, the proposed method can run faster than real-time for time horizons of several orbits, enabling a high level of autonomy in orbit

A Two-Stage Batch Algorithm for Nonlinear Static Parameter Estimation

A two-stage batch estimation algorithm for solving a class of nonlinear, static parameter estimation problems that appear in aerospace engineering applications is proposed. It is shown how these problems can be recast into a form suitable for the proposed two-stage estimation process. In the first stage, linear least squares is used to obtain a subset of the unknown parameters (set 1), while a residual sampling procedure is used for selecting initial values for the rest of the parameters (set 2). In the second stage, depending on the uniqueness of the local minimum, either only the parameters in the second set need to be re-estimated, or all the parameters will have to be re-estimated simultaneously, by a nonlinear constrained optimization. The estimates from the first stage are used as initial conditions for the second stage optimizer. It is shown that this approach alleviates the sensitivity to initial conditions and minimizes the likelihood of converging to an incorrect local minimum of the nonlinear cost function. An error bound analysis is presented to show that the first stage can be solved in such a way that the total cost function will be driven to the optimal cost, and the difference has an upper bound. Two tutorial examples are used to show how to implement this estimator and compare its performance to other similar nonlinear estimators. Finally, the estimator is used on a 5-hole Pitot tube calibration problem using flight test data collected from a small Unmanned Aerial Vehicle (UAV) which cannot be easily solved with single-stage methods.Comment: Accepted by AIAA Journal of Guidance, Control and Dynamics, Dec 201

Entrance of Prospective Teachers to Initial Teacher Education and Stereotypes Around the Teaching Profession: Experiences From Eritrea

The inquiry framed into an action research strategy was initiated in the College of Education (CoE) at the Eritrea Institute of Technology, a major Initial Teacher Education (ITE) center in the country. The paper tried to answer the question: How do prospective-teachers happen to attend in the CoE? The paper also sheds light on the prevailing stereotypes around the teaching profession. The methodological and analytical framework of the research lies in the premise of teaching as a reflective practice. Qualitative data were gathered through focus group discussions (FGD) and in-depth interviews involving 126 participants comprising the leadership, educators and students of the college in the academic year 2012/2013. The FGDs and interviews were audio and video recorded, transcribed and thematically analyzed. The findings reveal that learning process in the CoE is influenced by a myriad of systemic, institutional and attitudinal issues that intersect and further complicate the already problematic nature of teaching. The nature of the admission of the prospective teachers to the CoE and the stereotyped public views toward the CoE vis-à-vis the teaching profession are among the major stumbling block that affect the classroom practice at the college and beyond. As part of the researchers’ commitment to follow a collaborative action research cycle, the findings were shared with educators and learner-teachers in ITE institutions. Areas of intervention were identified and the college is engaged in a number of collaborative activities involving its staff, local and international partners in ensuring the provision of quality teacher education in the country. Keywords: admission process, teaching profession, stereotypes, collaborative action research

Rüdiger Görner, Franz Kafkas akustische Welten

Le 13 décembre 1911, en rentrant d’un concert, Kafka écrivit dans son journal : « la musique écoutée élève naturellement un mur tout autour de moi, et la seule influence musicale que je subis durablement est la suivante : ainsi enfermé, je ne suis pas le même qu’en liberté ». Le rapport que Kafka entretient avec le monde musical est donc relativement ambigu ; bien qu’il soit en mesure d’apprécier la musicalité de la langue et qu’il ait une oreille formée à la mélodie grâce à sa très bonne con..