U.S. Army Redstone Test Center

The signal to noise ratio and corresponding visibility of power cables as seen by military aircrafts is critical for crew safety. During low altitude operations, rotorcraft systems must be able to navigate these power lines during flight. Many of these military missions are flown at night which means the reflective bands including the visible, near infrared and short-wave infrared do not provide sufficient light. However, the emissive bands of the mid-wave infrared (MWIR) and long-wave infrared (LWIR) can be used to distinguish the location of these wires. LWIR sensors are typically used for pilotage applications. In both the LWIR and MWIR, the signal to noise depends on the wire emissivity and reflectivity as well as the ground and sky background path radiance. The signal to noise ratio is strongly dependent on the elevation of the viewing angle. In this paper, we model the signal to noise ratio as a function of elevation viewing angle using wire reflectivity and emissivity as well as MODTRAN calculations for path radiance. We also take MWIR and LWIR measurements to compare these two bands to the modelling results. We provide a summary of both model and measurements and make conclusions.

Multiple Degree of Freedom (MDOF) excitation systems and MDOF vibration control systems continue to improve, and are now standard equipment in many dynamic test laboratories. Determination of an input specification for such MDOF systems is critically dependent on properly acquired field data. Validation of field data will be discussed and demonstrated employing the same transformation tools used in both transformation-based 6-degree-of-freedom (6-DOF) vibration control and generalized MDOF vibration specification development (VSD).

This paper discusses the use of social media and cloud computing technologies to facilitate the collaboration and communication in enterprise-wide workflow processes. It presents a use case analysis of the US Army Test and Evaluation Command (ATEC) test program management to demonstrate how cloud computing and social media could streamline pre-existing, highly serialized, enterprise-wide workflow processes. The resulting optimizations to the monitoring, reporting, and control aspects will lead to situational awareness information being available to senior leadership with far fewer intermediary, human-in-the-loop steps. These optimizations, when combined with social networking tools and a common integrated working environment for program artifacts, may result in an increase to productivity across all levels of the organization.

Matching measured and modelled signal to noise ratio and corresponding visibility of power lines in the mid-wave and long-wave infrared. The signal to noise ratio of the wire depends on emissivity, reflectivity and the background atmosphere and ground path radiance.

Modulation transfer functions (MTFs) describe how a sensor system transfers spatial frequencies of a scene through an imaging system. For infrared systems, lab measurements are performed in a laboratory setting with a collimated source and a tilted edge target. This method is the standard way to measure a sensor’s performance metric. When these sensors are used for practical applications in the field, factors such as focus, atmospheric turbulence, and path radiance limit the performance of the system. These environmentally induced blurs need to be considered when designing sensor systems to ensure the required performance is met. The effects of these factors on the sensor’s performance can be quantified by measuring an MTF while in the field. By matching laboratory and static field MTFs, the effects of other blurs can be isolated, such as platform dynamics, vibration, and atmospheric turbulence, which will affect the performance of the system. To obtain a field MTF that matches one measured in the laboratory, the variable field conditions need to be well controlled. The effects of MTF target nonuniformity, tilt angle, illumination spectra, integration time, dynamic range, and number of pixels on target were explored as possible environmental factors affecting the quality of field MTF measurements.

Prior work has shown that the masked target transform volume (MTTV) clutter metric provides a measure of scene clutter that better correlates to measured probability of detection for human observers than several previously published clutter metrics. Several factors involved in using the MTTV to assess clutter in imagery are discussed here. A previously published modification to the MTTV metric to provide a normalized output value comparable across different image sets regardless of scene size is reviewed. Initial MTTV development required knowledge of a scene's target signature and produced an unbounded metric value. Metric behavior is discussed for the case in which an average of several target signatures is used in place of a specific target signature. This allows the MTTV to be calculated for images that do not contain a target. It is shown that the user may trade computational efficiency with metric accuracy to suit a particular application. The sensitivity of the metric to variations in image noise level, target segmentation error, and viewing distance are also presented.

Electric field measurements for an electromagnetic wave excited from a log-periodic dipole array at two separation distances on a finite slotted circular cylinder are compared to an analytical model of a plane wave on an infinite slotted circular cylinder. The four foot diameter cylinder cross section is used to represent the cross section (1/2 scale) of an Army Blackhawk helicopter. The frequency range of interest is in the Very High Frequency (VHF) band where the first resonances of the cavity occur. Transverse Magnetic (TM) and Transverse Electric (TE) polarizations are considered.

The intensity of objects in the infrared is an important quantity for a number of applications. Intensity in watts per steradian is the parameter that is used to describe either small targets or targets that are far away. Intensity is used because these cases are usually presented to a detection sensor where the object is smaller than the sensor detector angular subtense, a situation known as an “unresolved target.” In the military, unresolved targets can be rocket-propelled grenades, man-portable air defense threats, enemy aircraft at long range, or even ground vehicles that are being engaged by ground-to-ground or air-to-ground missiles. Typical “resolved target” metrics such as root-sum-squared differential temperature do not work well for unresolved targets. In addition, a given target intensity coupled with range, atmospheric transmission, and sensor noise equivalent irradiance can provide a quick signal-to-noise estimate of a particular sensor against a particular target. Target intensity can even be a measure of how visible ones platform is to other sensor and can be used to reduce platform signatures. Measurement of intensity is always a difficult procedure, where there is typically a sensor that does not encompass all aspects of measurement parameters. For example, there are very few radiometers that include high-resolution spatial measurements with high-resolution spectral measurements with high-resolution temporal measurements, not to mention polarization. For the few systems that exist that can provide a simultaneous measurement with most of these parameters, the cost is prohibitive. Usually, a spectral radiometer will provide high spectral resolution with no spatial information and a slow temporal rate. These measurements are common. In the case we describe here, the intensity measurement is taken broadband in the midwave or longwave infrared regions with good spatial resolution. This measurement provides a band integrated intensity measurement. We describe an approach for sensor calibration and object intensity measurement that can be used for broadband sensors applications.

Abstract As multiple degree-of-freedom excitation systems continue to evolve and become standard hardware in many dynamic test facilities, there continues to be a lag in the development of associated spectral density based vibration specifications. The following discussion is centered on the development of a six-degree-of-freedom spectral density matrix based vibration specification and various comparisons to traditional single-degree-of-freedom, combined three-degree-of-freedom, and synthesized six-degree-of-freedom specification results, all computed from a common set of field data and assumptions of a common mission scenario. Laboratory test results and general observations are presented.

A comparatively “low cost” electromagnetically “quite” environment is desired to address needs for aircraft noise floor testing. A 100 ft. X 150 ft. X 70 ft. cage was previously constructed using square 4 inch wire mesh. Although still in use, the ability of this facility to provide shielding from the external electromagnetic environment has degraded due to weathering of the wire mesh (rust). We intend to refurbish this facility using stainless steel mesh. The measured frequency-dependent isolation effectiveness of three different square meshes (4 inch, 2 inch and 1 inch) is compared to calculations of the same. Our current model is that proposed by LEE [1], wherein a simple approximate formula for the mesh admittance and isolation is derived in terms of the mesh periodicity, wire diameter, and wavelength.

With the move towards fly-by-wire flight control systems for rotorcraft, pilot inceptors are no longer physically connected to the mechanical hardware of the aircraft. This has allowed the move to smaller, lighter, side-mounted controllers, which typically lack a mechanical connection between the pilots' inceptors. Such controllers can be electronically linked using active inceptors, however this adds cost and weight over passive inceptors. The objective of the work presented in this paper is to assess the impact of linked versus unlinked cyclics on Army helicopter aircrew coordination. To do this, a piloted simulation was conducted in the NASA Ames Vertical Motion Simulator using both Mission Task Element type maneuvers, as well as more operationally relevant mission vignettes. The simulator was configured with two side-by-side pilot stations with sidestick controllers which could be configured to operate in either a linked or unlinked configuration. During each task, a control transfer from the pilot flying to the pilot not-flying was either forced or induced, and subsequently the pilots were asked to answer a series of questions and rating scales related to predictability, awareness, and acceptance. Results of the study showed that in all cases, pilots preferred the linked cyclic controller configuration, which received better predictability, awareness, and acceptance ratings. In addition, the linked cyclic controller configuration had shorter-duration simultaneous input events (both pilots moving their inceptors to control the aircraft at the same time) compared to the unlinked cyclic controller configuration.

In implementing electromagnetic vulnerability (EMV) testing on operational manned and unmanned air and ground vehicles fielding a variety of avionics and communication systems, the test as spelled out in MIL-STD-464D [1] and ADS-37A-PRF [2] requires test labs to operate the high-power source amplifiers/antennas very near the test item to reach required peak and RMS test levels for Electromagnetic Environmental Effects (E3) testing. Questions naturally arise concerning the efficacy of such testing with respect to both the manner of coupling of the fields to the electronics system of the air or ground vehicle as well as the levels required to achieve reasonable confidence in the coupling effect.

The generation of Gaussian noise with a specific auto spectral density (ASD) is a well-documented process employed in drive signal generation in vibration control applications. In recent years, vibration control system vendors have introduced the ability to modify the probability density function (PDF) characteristics associated with the reference ASD, yielding a non-Gaussian drive. The specific parameter defining this process is kurtosis. This paper will discuss concerns with this practice in terms of synthesizing a time history with dissimilar PDF characteristics to that of the measured data upon which the original ASD and kurtosis characteristics were based. An example is discussed from both statistical and fatigue perspectives.

This paper provides results of a laboratory experiment designed to illustrate the theoretical control considerations for an over-actuated excitation system. The experiment is based on control of a beam pinned at one end providing a single rotational degree of freedom and excited by two electrodynamic actuators. Control is achieved through implementation of two different control reference techniques: (1) reference based on linear acceleration autospectral densities (ASD) and cross-spectral densities (CSD) using linear accelerometer feedback and (2) reference based on an angular acceleration ASD using estimates of angular acceleration as feedback. Correlations to the theoretical based predictions were conducted based on common measurements of both linear acceleration and estimates of angular acceleration acquired during each trial.

Multiple-degree-of-freedom (MDOF) excitation systems vary widely in performance, size, actuator selection, and general geometric configuration. When acquiring an MDOF excitation system it is imperative that the test objectives be clearly defined and performance criteria demonstrated prior to system integration. Development of a general purpose 6-DOF system will be illustrated from establishment of a general scope of work, through a detailed design effort, to ultimate integration of the system into a dynamics laboratory.

MIL-STD-464D dictates field strengths greater than 5000 V/m in certain ranges of the frequency spectrum. Achieving these field strengths in the far-field region often requires unrealistically high input power -almost 10 MW in some cases- and thus requires testing to be conducted in the near-field region. To meet these field strengths, pyramidal standard gain horns are often used in electromagnetic compatibility (EMC) testing for their wide bandwidth, ability to generate high gain, and ability to tolerate large amounts of input power. Despite the high gain and high input power tolerance of these antennas, they still cannot achieve the required field strength in the far-zone and therefore must be used in the near-field (Fresnel) region of the antenna. Due to this, our group has placed an increased focus on modeling the near-field gain of pyramidal horn antennas in commercially available EM solvers as well as analytically calculating the near-field gain in MATLAB. This issue and the subsequent analysis of similar pyramidal standard gain horns are examined in detail in (Carroll et al., Near-Field Analysis of Pyramidal Standard Gain Horns) which is submitted to the 2025 IEEE APS conference. In this paper, the Narda 646 standard gain horn is examined.

A directional control margin investigation of the MH-60M Black Hawk helicopter was conducted to address the loss of directional control when operating at high density altitudes and high gross weights. This paper will discuss the flight test techniques used to assess directional control margin, the process for determining gross weight for flight testing at high density altitude, and resolution of the loss of directional control on the MH-60M. Additionally, low density altitude, low gross weight, and low power flight tests were performed to ensure adequate right directional control margin remained after implementation of changes to improve the loss of directional control at high density altitudes and high gross weights. A relationship between power required and directional control margin was established. Based on that relationship, a flight test methodology was developed to successfully quantify the directional control margin (DCM) of the MH-60M in stabilized hover and in the low airspeed flight regimes.