George G. Koenig

Visibility Enhancement in Rotorwash Clouds

Enhancing vision in rotorwash dust and snow clouds using remote sensing devices would improve the safety of helicopter operations. Our approach is to simulate remote sensor performance by modeling brownout cloud microphysical conditions. We use computational fluid dynamics techniques to model rotorwash, assuming incompressible and laminar flow, to develop the nearfield and farfield flow around a rotorcraft of given weight and configuration. We are developing two phase flow techniques to incorporate dust particles into the flowfield. Currently, stochastic techniques are being used to simulate particle entrainment in the boundary layer, with ongoing research to model entrainment using more realistic boundary conditions of turbulent flow impinging on a porous, erodible bed. Sensor signal performance is being simulated with MODTRAN, driven by the synthetically created cloud particle size distribution and concentration.

Overview of Mount Washington Icing Sensors Project

NASA, the FAA, the Department of Defense, the National Center for Atmospheric Research and NOAA are developing techniques for retrieving cloud microphysical properties from a variety of remote sensing technologies. The intent is to predict aircraft icing conditions ahead of aircraft. The Mount Washington Icing Sensors Project MWISP), conducted in April, 1999 at Mt. Washington, NH, was organized to evaluate technologies for the prediction of icing conditions ahead of aircraft in a natural environment, and to characterize icing cloud and drizzle environments. April was selected for operations because the Summit is typically in cloud, generally has frequent freezing precipitation in spring, and the clouds have high liquid water contents. Remote sensing equipment, consisting of radars, radiometers and a lidar, was placed at the base of the mountain, and probes measuring cloud particles, and a radiometer, were operated from the Summit. NASA s Twin Otter research aircraft also conducted six missions over the site. Operations spanned the entire month of April, which was dominated by wrap-around moisture from a low pressure center stalled off the coast of Labrador providing persistent upslope clouds with relatively high liquid water contents and mixed phase conditions. Preliminary assessments indicate excellent results from the lidar, radar polarimetry, radiosondes and summit and aircraft measurements.

Evaluation of three helicopter preflight deicing techniques

Procedures for preflight deicing of helicopters have not been refined nor standardized. Parked helicopters are often exposed to weather, allowing freezing precipitation and snow to accumulate on airframe and blade surfaces. Unless removed, snow and ice may linger after precipitation ends, grounding aircraft for hours to days, depending upon temperature. Newer helicopters with comlposite blades and fuselage components are susceptible to damage corn deicing operations because thermal and mechanical damage can cause delamination. In addition, glycol-based deicing fluids may cause corrosion of critical rotor head components. Therefore, there is a need to develop different ground deicing techniques for helicopters. This paper describes an experimental evaluation of the use of infrared radiation, hot water and hot air to deice helicopters before flight. The purpose of the experiment was to evaluate the effectiveness of each deicing method, and to assess the potential themial effects of each on rotor blade composites. Our greatest interest was the potential for using infrared radiation as a deicing agent, a technique that has been used to deice fixed-wing aircraft, but not helicopters. Introduction and Problem Hangared helicopters are protected from weather. However, helicopters exposed to ,weather during military, search and rescue, medevac, anld oil rig supply operations allow freezing precipitation and snow to accumulate on airhame and blade surfaces when parked. Adhering snow and ice may linger after a storm passes, grounding aircraft for hours to days, unless frozen precipitation is manually removed. Reports that manual deicing methods can require up to four hours to prepare a single aircraft for flight, and the inefficiency of manual methods, justifies the need for finding better methods. Modem helicopters are mor’e likely to be damaged by ice and snow removal techniques than are fixed-wing aircraft because large portions of rotor blades and fuselage surfaces are constructed of composites. Composites are susceptible to damage from physical impact, scraping, high temperatures, and rapid thermal cycling. In addition, glycol deicing fluids may corrode helicopter rotor heads and wash lubricants from bearings. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the IJnited States. Boots and covers are occasionally used to protect helicopter components from ice and snow on the ground. For example, covers for blades, rotor heads, wind screens, tail rotors, engine inlets and, as on fixed-wing aircraft, pitot covers, are often used. However, reports of freezing of covers to aircraft surfaces make them less practical than desired. In addition, their use requires knowledge that freezing or frozen precipitation may occur when the aircraft is parked. Unless forecasts of freezing precipitation are very reliable and precipitation probabilities are high, aircraft are unlikely to be covered prior to a storm resulting in snow or ice-covered aircraft requiring deicing. This paper describes an experimental evaluation of the use of in&red radiation, hot liquid, and hot air to deice Army Blackhawk helicopters before flight. It also describes the utility of a portable ice imager system for use in deicing procedures. The purpose of the experiment was to identify deicing techniques available for helicopters, to select and evaluate the effectiveness of several methods, and to assess the potential thermal effects of each on rotor blade composites.

Preliminary Analysis of X-band and Ka-band Radar for Use in the Detection of Icing Conditions Aloft

ABSTRACT NASA and the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) have an on-going activity to develop remote sensing technologies for the detection and measurement of icing conditions aloft. Radar has been identified as a strong tool for this work. However, since the remote detection of icing conditions with the intent to identify areas of icing hazard is a new and evolving capability, there are no set requirements for radar sensitivity. This work is an initial attempt to quantify, through analysis, the sensitivity requirements for an icing remote sensing radar. The primary radar of interest for cloud measurements is Ka-band, however, since NASA is currently using an X-band unit, this frequency is also examined. Several aspects of radar signal analysis were examined. Cloud reflectivity was calculated for several forms of cloud using two different techniques. The Air Force Geophysical Laboratory (AFGL) cloud models, with different drop spectra represented by a modified gamma distribution, were utilized to examine several categories of cloud formation. Also a fundamental methods approach was used to allow manipulation of the cloud droplet size spectra. And an analytical icing radar simulator was developed to examine the complete radar system response to a configurable multi-layer cloud environment. Also discussed is the NASA vertical pointing X-band radar. The radar and its data system are described, and several summer weather events are reviewed.

UAV Icing Flight Simulation

Unmanned Aerial Vehicles (UAVs) are necessary tactical tools for Army field commanders requiring surveillance, targeting aids, and communication links. Icing and freezing precipitation can create serious problems for Army UAVs. Though the Army UAVs were not initially flown in Kosovo between October and April because of icing, and flights were not launched when icing was forecast, 25% of UAV flights encountered icing. The Armys present icing avoidance approach is to not fly when icing is forecast. While this solves, in part, the problem of aircraft icing, it negatively impacts mission success. To explore the impact of icing on UAVs and the potential use of low weight, low-power remote sensing systems to allow UAVs and other aircraft to avoid or minimize icing conditions during flight, we have looked at the environmental conditions conducive to icing potential, sources of field measurements and models for characterizing natural icing conditions, and models that predict ice accretion on airfoils. Techniques have been developed to simulate ice accretion rates, type, and shape on airfoils for flights in natural icing conditions. This paper discusses our approach and simulation techniques and presents some preliminary results.

Smart weapons operability enhancement synthetic scene generation process

The smart weapons operability enhancement (SWOE) program has developed a synthetic scene generation process that incorporates formal experimental design, random sampling procedures, data collection methods, physics models, and numerically repeatable validation procedures. The SWOE synthetic scene generation procedure uses an assemblage of measurements, static and dynamic information databases, thermal and radiance models, and rendering techniques to simulate a wide range of environmental conditions. The models provide a spatial and spectral agility that permits the simulation of a wide range of sensor systems for varied environmental conditions. Comprehensive validation efforts have been conducted for two locations: Grayling, Michigan and Yuma, Arizona, and for two spectral bands: shortwave (3 - 5 micrometers ) and longwave (8 - 12 micrometers ) IR. The intended use of the validated SWOE process is synthetic battlefield scene generation. The users of the SWOE process are the smart weapons system designers, developers, testers and evaluators, including developers of automatic target recognition algorithms and techniques.

Spatial Analysis of Great Lakes Regional Icing Cloud Liquid Water Content

Abstract Clustering of cloud microphysical conditions, such as liquid water content (LWC) and drop size, can affect the rate and shape of ice accretion and the airworthiness of aircraft. Clustering may also degrade the accuracy of cloud LWC measurements from radars and microwave radiometers being developed by the government for remotely mapping icing conditions ahead of aircraft in flight. This paper evaluates spatial clustering of LWC in icing clouds using measurements collected during NASA research flights in the Great Lakes region. We used graphical and analytical approaches to describe clustering. The analytical approach involves determining the average size of clusters and computing a clustering intensity parameter. We analyzed flight data composed of 1-s-frequency LWC measurements for 12 periods ranging from 17.4 minutes (73 km) to 45.3 minutes (190 km) in duration. Graphically some flight segments showed evidence of consistency with regard to clustering patterns. Cluster intensity varied from 0.06, indicating little clustering, to a high of 2.42. Cluster lengths ranged from 0.1 minutes (0.6 km) to 4.1 minutes (17.3 km). Additional analyses will allow us to determine if clustering climatologies can be developed to characterize cluster conditions by region, time period, or weather condition. Introduction

Screening design for model sensitivity studies

This paper describes a different approach to sensitivity studies for environmental, including atmospheric, physics models. The sensitivity studies were performed on a multispectral environmental data and scene generation capability. The capability includes environmental physics models that are used to generate data and scenes for simulation of environmental materials, features, and conditions, such as trees, clouds, soils, and snow. These studies were performed because it is difficult to obtain input data for many of the environmental variables. The problem to solve is to determine which of the 100 or so input variables, used by the generation capability, are the most important. These sensitivity studies focused on the generation capabilities needed to predict and evaluate the performance of sensor systems operating in the infrared portions of the electromagnetic spectrum. The sensitivity study approach described uses a screening design. Screening designs are analytical techniques that use a fraction of all of the combinations of the potential input variables and conditions to determine which are the most important. Specifically a 20-run Plackett-Burman screening design was used to study the sensitivity of eight data and scene generation capability computed response variables to 11 selected input variables. This is a two-level design, meaning that the range of conditions is represented by two different values for each of the 11 selected variables. The eight response variables used were maximum, minimum, range, and mode of the model-generated temperature and radiance values. The result is that six of the 11 input variables (soil moisture, solar loading, roughness length, relative humidity, surface albedo, and surface emissivity) had a statistically significant effect on the response variables.

Smart Weapons Operability Enhancement Joint Test and Evaluation Program Grayling 1: preliminary results

The primary objective of the Smart Weapons Operability Enhancement (SWOE) Joint Test and Evaluation (JT&E) Program is to validate the SWOE Process for the Office of the Secretary of Defense. The SWOE Process is a physics based scene generation capability that will enhance the performance of future smart weapon systems for a global variety of battlefield environments. This process is focused on generating complex background environmental scenes, including targets, for a world wide range of battlefield conditions. The SWOE program is a DoD wide partnership incorporating capabilities from the Army, Navy, Marine Corps and Air Force. The principal thrusts of SWOE are to quantitatively define the environmental factors and processes and to provide the capabilities to measure, model, render and extrapolate their impact on smart weapon system performance. The Grayling I exercise is the first in a series of four coordinate field deployments focused on validation of the SWOE Process. This paper describes the experimental design, sampling plans, measurement efforts and summarizes preliminary results of the Grayling I exercise.

Direct detection polarimetric radiometer (DDPR)

Polarimetric signatures of terrain features and man-made objects have been measured using unique Direct Detection Polarimetric Radiometers (DDPR). The DDPRs are lightweight inexpensive systems operating at 35 and 94 GHz. Each system consists of a single antenna, amplifier, and a truncated cylindrical waveguide that directly measures Q, U, and V. The highly portable DDPRs are ideal for obtaining the Stokes vectors needed to study the physical characteristics of natural and man-made features. Field evaluations using the DDPR systems include measurements from an airborne platform over different terrain features and water, and ground based measurements of the polarimetric signature of grass, asphalt, buildings, and concealed munitions. The DDPR can function as a bistatic system by using an active source of polarization. Using this configuration and a soil chamber, we have investigated the effect of soil type and soil moisture on linear and circular polarization. This report will describe the DDPR and present the analysis of the airborne and ground based measurements, including the effects of soil type and soil moisture on sources of linear and circular polarization.