Vashon Island Fair Skies   http://www.vifs.org 
PO Box 1250            info@vifs.org
Vashon, WA 98070      (206)682-8638
Dedicated to restoring the pre-NextGen dispersed arrival paths and more optimized
profile descents at Seattle/Tacoma International Airport that had been in place since
the introduction of commercial aviation to the Puget Sound region, many decades ago. 


August 11, 2020 
Dear Port of Seattle Commission,
We're requesting the Port of Seattle make a procedural change in how the data from your system of port owned Larson Davis
831 noise monitors is collected and retained. This is particularly timely given that the contract with the vendor who provides
services associated with the monitors, L3Harris, is due for renewal as per Item 6e in today's commission meeting. 
Currently the Port does not retain the raw second by second measured sound level data but instead contracts the data
collection and analysis to the vendor L3Harris. The vendor periodically downloads this data and then purges it from the
monitors. They use this data to build a list of SELs (Sound Exposure Level) for overflight events at that monitor location along
with a set of noise statistics for the site. Nothing precludes the Port from also downloading a copy of their own raw second by
second data from the Port owned noise monitors before L3Harris purges it. Alternatively, if the Port's Noise Office wants to
retain a completely hands-off relationship with their own noise monitors, the vendor L3Harris could deliver the raw data with
the other processed data currently being supplied. This raw data amounts to ~62 MB/month (~40 MB compressed) per
monitor, which is tiny by today's standards.
At the UC Davis Aviation Noise & Emissions Symposium in March I spoke with L3Harris, who was a sponsoring vendor and had
a booth there. Samuel Carter, their Training & Solutions Manager, indicated it would be a simple modification of the
procedure to deliver the raw data with the processed results. The Port simply has to request it. I didn't ask, nor did he say, if
there would be an extra cost for that. However, again, this is Port owned data on Port owned noise monitors so the Port can
simply download this data themselves periodically before L3Harris purges it.
This raw data is absolutely essential for any rigorous analysis of the aviation noise levels at the site. As a real-world example, I
was looking over the processed data from last December and came across an interesting anomaly. Here is a map of six noise
monitor sites immediately North of the Airport including overflight event counts for December:

What's odd here is how small the event count at site #12 was. It was near the axis of the runways, as were sites 11 and 13,
yet had a much smaller event count. Site #1, on the grounds of the airport proper also had a low count. In that case the
overall background noise of the airport could drown out the signal from individual operations. Site #15 was laterally
separated from the runways which could explain its low count. However site #12 doesn't have a good explanation for being
so low.
By looking at the runway data and focusing on the triangle of sites North of the airport (#11, #12, and #13) we can see the key
difference for site #12.







Runway (Southflow)     Runway (Northflow) 
Site       16L       16C     16R       34L    34C     34R     Unknown 
SEA01    3676    970    2218     74     10     702    232 
SEA11    2344    306    31342    0      6       724    0 
SEA12    4750    236    304      0      16     778    0 
SEA13    228     48     24758    0      10     656    0 
SEA14    6446    1186   14692    0      10     790    160 
SEA15    308     160    498      2      0       12     0 
Unsurprising for December, Southflow was much more common than Northflow. In Northflow, these departures are high
throttle (i.e. loud) and the three sites give similar numbers, or at least the same order of magnitude. In Southflow however
something emerges. The big discrepancy with site #12 is due to 16R Southflow arrivals.
Site #11 is the most centered of the three and its numbers tell the story of runway use for Southflow arrivals. By a large
margin 16R, the "Third Runway", is the most commonly used. As an aside, during the legal battles over building the third
runway, the community was assured it would only be used in rare circumstances, but that's another story. So, site #12, being
East of the airport is the furthest from 16R, but we're talking about a two orders of magnitude reduction in events from Site
#11 to Site #12 even though Site #12 is only ~3300 feet East of Site #11.
That small separation shouldn't account for such a huge discrepancy. I made Public Records Request 20-19 to get the raw
data from site #12 for December to investigate what was causing this. The data came with this ominous warning:
"The vendor, L3Harris was able to extract the data. Please note that this is not data that the Port keeps inhouse
on its Noise Monitoring system. L3Harris has indicated that all future records we obtain from them
are subject to an additional fee that we would have to pass on to you."
With this data it became clear why site #12 was reporting so many fewer events.

For the purpose of this illustration, I'll cover a short period on the morning of 12/1/19:
Date/Time          Noise Monitor   Flight ID   Operation  Equipment   Runway   SEL 
12/1/2019 8:30:09   SEA12          DAL166    Arrival      A339        16L       85.47776989 
12/1/2019 8:30:58   SEA11          ASA85     Arrival      B739        16R       86.59586146 
12/1/2019 8:33:11   SEA11          ASA368    Arrival      B738        16R       86.13313923 
12/1/2019 8:35:07   SEA11          QXE2535   Arrival      E75L         16R       83.59008407 
12/1/2019 8:35:10   SEA12          ASA625    Arrival      B739        16L       83.32092607 
12/1/2019 8:36:32   SEA11          ASA169    Arrival      B738        16R       85.4135081 
12/1/2019 8:37:20   SEA11          KAL019    Arrival      B77W       16L       77.66649632 
12/1/2019 8:37:41   SEA12          KAL019    Arrival      B77W       16L       87.66999824 
12/1/2019 8:38:08   SEA11          ASA1017   Arrival      A320        16R       85.72240682 
12/1/2019 8:39:33   SEA11          CPZ5782   Arrival      E75S        16R       83.028042 
12/1/2019 8:41:02   SEA11          ASA894    Arrival      B738        16R       86.45152272 
12/1/2019 8:42:12   SEA12          QXE2433   Arrival      E75L         16L       81.04083749 
Note that only KAL019 was recorded by both SEA11 and SEA12 and were separated by about 21 seconds. These events are
attached to the sound level graph below, with the flights detected by SEA12 written in black above the peaks and the flights
only detected by SEA11 written in gray under the smaller peaks. So small in fact, that the algorithm did not consider them to
be events:




The issue here is the very high background noise level at this site, which causes the signal to not be sufficiently above the
ambient noise level to convince the software that it's an overflight.
Retaining the raw data from the Port owned noise monitors is critical, and instead allowing the data to be purged violates the
spirit, and perhaps the letter, of the Public Records Act (RCW 42.56).
We filed Public Records Request 20-314 asking for a copy of the proposed contract in item 6e, and we request that this item
be removed from today's Unanimous Consent Calendar until we've had a chance to review the changes to the contract.
Thank you,
David Goebel
President, Vashon Island Fair Skies