Posts Tagged ‘inm’

INM Version 7.0c and Floatplanes in Alaska

Thursday, January 5th, 2012

by Brad Nicholas

If you have not heard, the Federal Aviation Administration (FAA) just released Version 7.0c of its Integrated Noise Model (INM).  This update is almost entirely about database changes, and a lot of them, including:

  • Updated noise information for nineteen aircraft
    • Nine Airbus jets
    • Six props
    • Four helicopters
  • Sixty-eight changes to aircraft substitutions
    • Twenty-two new
    • Thirty-eight modified
    • Eight deleted
  • Eleven new aircraft
    • Five Cessna jets
    • Four Bell helicopters
    • Two single-engine floatplanes
  • Modified arrival profiles for twenty-one aircraft
    • Sixteen Airbus and Boeing jets (updated reverse thrust segment)
    • Five props (added final landing segment)

There are a few other changes, but you can find those in the release notes.  I’m an instructor for HMMH’s INM Training Course so I take an interest in any new releases, but there was something special about this one.  In the list above, I’m fairly confident that the thing that jumps out at everyone is the floatplanes.  Or maybe that’s just me.  Let’s do a little backstory here.

In June of 2007 I was at Willow Lake, Alaska doing noise measurements for a study of floatplane noise.  Willow Lake is just up the road from the now (in)famous city of Wasilla.  Each year, the frozen lake is used as the restart point for the Iditarod dog sled race.  It’s a scenic little lake, surrounded by forest with houses, cabins, and a community center along the shore.  It is also used by floatplanes.

Floatplane Departure, Willow Lake, AK

 The weather for the measurement program was great and the residents around the lake were friendly and helpful.  Folks in Alaska love their airplanes.  It is by far the most aviation-literate population that I have ever met.  Everyone seemed to be a pilot, have been a pilot, or at the bare minimum, have a pilot in the family.  Given the love of airplanes and the low operations levels (approximately twenty operations per day in-season), why was the study necessary?

In short, the floatplanes, particularly the de Havilland DCH-2, are loud and due to the size of the lake and proximity of the houses to the shore, the planes are quite close to residential locations when they are applying full thrust to get off the water.  Here’s a picture of a Beaver taking off from the deck of residence along the shore.

De Havilland DHC-2 Beaver Take-off, Willow Lake, AK

 At full throttle, that radial piston engine and whirling propeller produced maximum levels averaging 112 dBA at this location for northbound departures.  A single northbound DHC-2 departure per day would give a Day Night Average Sound Level (DNL) of 70 dB.  Actual average levels were quite a bit lower due to a much higher percentage of southbound departures and the fact that the lake is frozen most of the year.  Still, after experiencing this firsthand, I was impressed by the tolerance of the locals.
After the measurement program, it was time to model the average annual conditions for our report.  At that time INM 7.0 was the most current version and the DHC-2 was modeled using the GASEPV, a generic single engine piston aircraft with a variable-pitch propeller.  Unfortunately, that aircraft produced levels that were nine to twenty-three decibels too low compared to the measurements, depending on the location along the flight path.  To put twenty-three decibels in perspective, using that aircraft would be the same as using an accurate aircraft, but modeling one two-hundredths of the correct number of operations.
 After no small amount of work and worry, I ended up creating a user-defined aircraft by modifying the GASEPV to have a much longer take-off distance and increased source noise levels.  This produced a reasonable representation of the Beavers operating on the Lake.
Let’s jump back to 2012 and the release of INM 7.0c.  It has a new aircraft, a DHC-2 floatplane.  Let’s see how it compares on the most common departure path at Willow Lake.  The table below includes measured values and the INM 7.0c computed Sound Exposure Level (SEL) and take-off roll distances for the GASEPV (INM 7.0 representation of the DHC-2), my user-defined aircraft, and the new DHC-2FLT.
Item Description Measured GASEPV User-Defined DHC-2FLT
Site 1 SEL (dBA) near start of takeoff





Site 2 SEL (dBA) take-off “roll”





Site 3 SEL (dBA) just after take-off





Site 4 SEL (dBA) after take-off





Take-off Roll (ft)  





Well, nothing hits the measurements exactly at all points, but the user-defined aircraft and the new DHC-2FLT are clearly better than the old substitution.  Of course the user-defined aircraft was developed from precisely this particular set of measurement data so the agreement is not surprising.  The agreement with the new standard INM data is nice to see though.  The development of this data for the new DHC-2FLT will be detailed in a US DOT Volpe National Transportation Systems Center report which is pending publication (see the INM 7.0c release notes).
The discrepancies for the take-off roll portion are not entirely unexpected.  First, the measurements may slightly overstate the SEL by including some taxi noise.  Second, water is a hard reflective surface and the INM will underestimate the levels when the primary reflected path is off the water due to the inclusion of a soft-ground effect.  You can remove this effect for props in the INM, but it would do that at all sites which would throw off the results at Sites 3 and 4 where the soft-ground assumption is more appropriate.  Third, the measurements were of a limited number of aircraft which performed the majority of the operations on this particular lake.  The general fleet may be slightly different.
So there you have it, INM 7.0c is out and it has two new floatplanes.  This may not matter to most folks, but I can remember a few months back 2007 when this would have made my life a lot easier.

October 2011 INM Course

Wednesday, August 24th, 2011

by Brad Nicholas

HMMH’s is offering its fall Integrated Noise Model (INM) training course October 5-7.  Registration is open and space is available.  Check our website for registration details.  The course covers:

  • Airport noise terminology
  • Airport noise modeling basics
  • INM input
  • INM output
  • Several complete INM test cases

The vast majority of the course deals with the nuts and bolts of entering and editing model input, running the model, and handling the output.  Students get a lot of hands on practice.  If you plan on creating or reviewing airport noise contours, this course is for you.

I’ve been working with students in the INM course for nearly nine years.  We get a folks from a variety of backgrounds and I always enjoy helping them to learn something new.

INM Screen Capture

Environmental Smackdown – Aviation v. High Speed Rail

Monday, February 14th, 2011

by Mary Ellen Eagan

I’m inspired by a few recent events to pontificate on this subject; those events are:  (1) Joe Biden’s recent remarks on high speed rail (HSR) in the US, (2) Greg Principato’s response, and (3) a recent session at the TRB Annual Meeting: “Environmental Tradeoffs of Aviation and High Speed Rail”.

First, let me be clear:  I do not think that one mode of transportation is “better” than another.  In fact, I’m quite sure that we have a need for both and our focus should be on complementarity, not competition.  That said, high speed rail advocates in the U.S. are making statements that unequivocally claim that high speed rail is “better for the environment”.  But let’s check the facts, as far as I’ve gathered them (admittedly, a somewhat cursory review):

  • Capacity:  Matt Coogan and others have prepared a comprehensive case study of the impact of high speed rail on aviation capacity in ACRP 31:  Innovative Approaches to Addressing Aviation Capacity Issues in Coastal Mega-regions.  They conclude that while introduction of Acela Amtrak service between Boston and New York has reduced passenger traffic by about 1/3, the number of flights between the two cities has dropped by only about six percent – shuttle operators have just adapted by substituting smaller aircraft on those routes to meet the schedule demand.
  • Noise:  Noise assessments for aviation and high speed rail both rely on Day Night Average Sound Level, but the similarities end there.  The FRA’s HSR Guidance Manual determines impact on noise sensitive communities by comparing project levels to existing noise levels to determine two categories of impact (moderate and severe), while the FAA’s Order 1050.1E determines impact by identifying noise-sensitive land uses that are projected to experience an increase in noise of 1.5 dB or more in those areas already exceeding DNL 65.  To make matters even more complicated, people appear to respond differently to aircraft noise than rail noise (they are more annoyed by it); on the other hand, if the rail vehicle in question is moving fast enough to cause startle (i.e., HSR), it’s not clear whether annoyance reaction is more like aircraft than rail.  Ruth Mazer and I gave a presentation at TRB comparing aviation and HSR in the Boston-New York Acela corridor, using both the FRA methodology and the FAA’s Integrated Noise Model.  We estimated that the number of people exposed to Sound Exposure Levels (SELs) from aircraft flying BOS-NYC high enough to cause speech disturbance (85 dB) ranges from 1,000 to 1,500 (depending on runway, flight path, aircraft type, and airport); whereas the number of people exposed to the same level on the BOS-NYC route is 12,000.  On the other hand, there are close to 30 shuttle flights per day in each direction and only 10 trainsets.  Is it better to expose the same 1,000 people to excessive noise 60 times per day or twelve times as many people only 20 times per day? 
Source: EU Position Paper On Dose Response Relationships Between Transportation Noise And Annoyance, 2002

Source: EU Position Paper On Dose Response Relationships Between Transportation Noise And Annoyance, 2002:

  • Air Quality:  Mikhail Chester from UC Berkeley also gave a presentation at TRB entitled, “Life-Cycle Assessment of High Speed Rail:  Total Environmental Accounting”, in which he compared the total air quality outputs from automobiles, aviation, and HSR.  LCA includes not just the operation and maintenance of the vehicles, but the infrastructure development and energy production.  Two interesting figures are presented below, which demonstrate that although emissions per passenger kilometer traveled (PKT) is highly dependent on vehicle loading, HSR consistently produces less CO2 than aviation only when it is assumed that the HSR uses “clean” fuel, and is not a clear “winner” over aviation when comparing NOx.  More detail on Mikhail’s research is here.
Lifecycle Greenhouse Gas Emissions, Source: Mikhail Chester, 2011

Lifecycle NOx Emissions, Source: Mikhail Chester, 2011


Lifecycle NOx Emissions, Source: Mikhail Chester, 2011

Lifecycle Greenhouse Gas Emissions, Source: Mikhail Chester, 2011

I look forward to your responses, and to seeing some real data – especially noise – on this subject.