IEEE Technology and Society Magazine - Winter 2013 - 61

signatures of interest is "challenging," to put it mildly. But this type
of analysis problem is of increasing
interest in both the scientific and
engineering communities.
In one regime, the sensor network is managed and calibrated
under the control of an external
entity, and the data are considered reliable. This is the case for
the academic seismic network that
complements and supplements the
seismic monitoring stations being
installed to verify compliance with
the Comprehensive Test Ban Treaty
(CTBT). But we are interested in
considering cases where the sensor
network is heterogeneous and not
centrally managed.
The Quake Catcher Network [10]
is an example of exploiting existing
sensors. The QCN team collects
accelerometer data from laptops
and mobile devices, and provides an
interesting opportunity to field-test
different data collection approaches
and robust analysis algorithms.
If the technical PTM community
tracks ongoing data mining efforts
in the scientific and commercial
domains, then (we suspect) PTM
efforts likely can implement and
adopt proven techniques, rather than
having to invent new tools.

Standards Problem
Incorporating data from a diverse
and evolving suite of sensors will
be greatly facilitated if uniform formatting standards were applied to
both data and metadata. At present,
different smartphone apps generate
data files in a wide diversity of formats. One approach for generating
uniform data sets would be to run
PTM software on each device that
produces PTM data, but this in turn
requires a global coordination of
the PTM effort. Another approach
is to have the servers that harvest
and distribute PTM information
take on the task of bringing all data
into a common format. This is an
issue with a scope that extends far
beyond the PTM context, and that
must be confronted and eventually

solved by the "ubiquitous sensors"
engineering community.

Privacy Issues: Anonymity
and Retribution
If PTM is to succeed, participating individuals must be protected
from any retribution, retaliation, or
pressure as a consequence of their
involvement. The exposure of any
individual will depend on the extent
to which a PTM sensor is directly
associated with that person, and
on the political and social situation
within their country. For example
one could imagine an "adopt-asensor" approach, where interested
individuals contribute to a fund that
acquires and installs networked
sensors that have no direct association with any particular individual.
In that scheme, supporting PTM
would be akin to directly contributing cash to a political campaign.
The more subtle issue is how to
deal with sensors that are attached
to or are an integral part of a personal computing device, for which
location reporting will be an
essential ingredient for properly
interpreting the PTM data. This
becomes an issue of individual
choice, and calls for an evaluation of personal exposure vs. participatory activism. The tradeoff
between the benefits of providing
location information vs. privacy
concerns is an ongoing topic of
public discourse, and PTM is but
one facet of this broader issue.
The issue of concern is the combination of location and/or other
identifier information with the
identity of the individual who is
supplying or facilitating the generation of PTM data. Given the principle of open data access, the PTM
sensor location information could
be combined with other information (such as cell phone records)
to determine which individual
provided the PTM data, even if
the metadata contain no explicit
identifiers. The ubiquitous sensor
concept is already off and running, and the PTM aspect will be a

IEEE TECHNOLOGY AND SOCIETY MAGAZINE

wINTEr 2013

minor consideration in this broader
issue. But PTM can certainly benefit from the technical solutions to
this problem.
If the location information in the
PTM database can be "jittered" so
as to obscure the sender's precise
location, while still retaining the
PTM information of interest, we
can imagine the PTM contributor
hiding in plain sight, in the clutter
of other cell phone users. The QCN
does attempt to preserve privacy of
its participants by fuzzing out the
exact location of their sensors, for
example. This requires an adequate
density of non-participants.
Another potential approach
to ameliorating this location and
attribution problem would be to
determine whether the PTM data
need to be associated with a sensor's location, or whether some
extracted and interpolated information (say the CO2 concentration
at ground level) might be the publically available PTM product. we
might term this "PTM anonymization by analysis".
One potentially interesting technical solution to the sensor location
and attribution problem through
intercepted traffic would be to
provide a PTM data pathway that
circumvents the local internet. A satellite communication system would
accomplish this. For low-bandwidth
sensors, a relatively simple relay satellite (that stores received data and
then retransmits to a set of downlink receive stations) would suffice. Establishing a PTM capability
within a not-entirely-trustworthy
country would then simply require
local citizens to obtain and install
sensors that transmit their data upon
being prompted by the PTM relay
satellite. If these PTM sensors were
solar or battery powered, they would
be locally "off the grid" entirely.

Incentivizing Enduring Public
Engagement in PTM
The red Balloon Challenge that
DArPA conducted [11] in 2009
arguably showed as much about
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Table of Contents for the Digital Edition of IEEE Technology and Society Magazine - Winter 2013