1 Sep 2020

PUBLICATION NOTICE: Preliminary Measurements on the Geography of Urban VHF Radio-Frequency Noise

Abstract: Radio-frequency (RF) noise has typically been measured at a handful of fixed, representative locations within the urban environment (Achatz, Lo, Papazian, Dalke, & Hufford, 1998; Achatz & Dalke, 2001; Dalke, Achatz, Lo, Papazian, & Hufford, 1997; Wepman & Sanders, 2011; Wagstaff & Merricks, 2005; Spaulding & Disney, 1974). In this work, we discuss the development of a mobile RF noise measurement system and the necessary geospatial and statistical post-processing techniques required to characterize the variations in noise on the street-scale in the VHF sections (60 – 300 MHz) of the spectrum. We discuss the design of our mobile noise measurement system, with special focus on the choice and calibration of preselection filters and preamplifiers necessary to reliably measure low RF noise levels while avoiding intermodulation distortion problems that arise in an environment with many strong emitters. Additionally, we describe post-processing techniques developed to reliably merge and interpolate the RF data with geolocation data which are collected on two very different (microsecond and multisecond, respectively) timescales. We use a preliminary urban dataset from Boston, MA to show that the geo-statistical properties of RF noise power can vary appreciably over street-scale distances, and that these spatial variations are repeatable over tactically relevant times.

11 Aug 2020

PUBLICATION NOTICE: The Urban Ground-to-Ground Radio-Frequency Channel: Measurement and Modeling in the Ultrahigh Frequency Band

ABSTRACT:  Ground-to-ground radio communication and sensing within the urban environment is challenging because line of sight between transmitter and receiver is rarely available. Therefore, radio links are often critically reliant on reflection and scattering from built structures. Little is known about the scattering strength of different buildings or whether such differences are important to the urban ground-to-ground channel. We tested the hypotheses that (1) diffuse scattering from built structures significantly impacts the urban channel and (2) scattering strength of urban structures varies with surface roughness and materials.  We tested these hypotheses by measuring urban channels in Concord, New Hampshire, and Boston, Massachusetts, and via channel-modeling efforts with three-dimensional representations of the urban environment. Direct comparison between measured and modeled channels suggest that both of these hypotheses are true. Further, it appears that ray-tracing approaches underestimate the complexity of urban channels because these approaches lack the physical processes to correctly assess the power incident on and scattered from built structures. We developed a radio-geospatial model that better accounts for incident power on both directly visible and occluded buildings and show that our model predictions com-pare more favorably with measured channels than those channels predicted via typical ray-tracing approaches.

18 Jul 2017

Army Corps, Metropolitan Washington Council of Governments to start study on ways to protect vulnerable assets from coastal flooding

Baltimore District signed an agreement July 18 with the Metropolitan Washington Council of Governments to begin an approximately $3-million, three-year study on possible ways to address coastal flooding and storm damage across more than 57 square miles in the District of Columbia and surrounding areas of suburban Maryland and northern Virginia. As part of this study, the team will investigate flood risk and identify ways to help protect vulnerable assets upon which the region relies, like local governments, businesses, institutions and water, energy and communication utilities; transportation hubs; federal buildings and military installations; national security facilities; and significant national monuments and cultural treasures.

18 Jun 2014

Army Corps of Engineers Joins City Agencies and FEMA in Debut of Nation’s First Urban Post-Disaster Housing Prototype in Brooklyn

Officials from the U.S. Army Corps of Engineers, New York District, recently joined Commissioners Joseph F. Bruno, New York City Office of Emergency Management, Feniosky Peña-Mora, New York City Department of Design and Construction, and officials from the Federal Emergency Management Agency in a ribbon-cutting ceremony in Brooklyn celebrating the completion of emergency prototype housing units designed to quickly resettle large numbers of people in urban areas after a major coastal storm or disaster. It is the only system of its kind in the U.S.

8 Apr 2013

Going Green: Restoring salmon to an urban park

PORTLAND, Ore. -- Crystal Springs Creek is one of thousands of small streams flowing through the Pacific Northwest. Most provide ideal habitat for fish, but this creek has not supported fish passage for about 40 years. "We have accounts of salmon dating from the 50s, 60s," said Ronda Fast, Environmental Program Coordinator, Portland Bureau of Environmental Services.