CEDAR email: Dr. John M. Holt: Obituary and Appreciation

[Phil Erickson]

To the CEDAR Community:

We are sorry to report that Dr. John M. Holt, a scientist and observational
pioneer in the geospace remote sensing group at MIT's Haystack Observatory,
passed away on April 15, 2025.  John leaves a lasting legacy within the
field of remote sensing radar-based observations of Earth's ionosphere and
thermosphere.  His work remains highly influential for incoherent scatter
radar, as the most comprehensive and incisive method for full altitude
profiling of the ionosphere, along with seminal tools for archiving and
retrieval of diverse ground-based upper atmosphere scientific observations
spanning many decades.

John earned his Bachelor's degree in physics from Harvard University in
1963, followed by both a Masters' degree (1964) and Ph.D. (1970) in physics
from Yale University.  After initial work as a software contractor, he
transitioned to a position at MIT's Lincoln Laboratory.  During this
timeframe, John began his involvement with the atmospheric sciences group
at MIT's Haystack Observatory in radar remote sensing efforts within a
group led (and founded by) John Evans.  This was later followed by a
position directly at Haystack in 1980.  John was a lecturer at MIT from
1983-2000 and was appointed to the Principal Research Scientist rank at
MIT, equivalent to faculty tenure status, in 1991.

Almost immediately on arrival at Haystack, John began to apply a sharp
mathematical eye to analyzing data from the Millstone Hill incoherent
scatter radar, quickly collaborating with former Haystack director Joe
Salah on a landmark and highly cited 1974 Radio Science paper on
radar-derived neutral winds in the thermosphere. John's subsequent more
than 3 decade long career as a radar technical expert and systems leader,
working closely with John Foster, spanned the core era of Millstone Hill
radar innovation, and helped maintain Haystack's prominence in the
incoherent scatter radar world.  Together with Evans, Foster, Salah, and
the Haystack geospace research team, John originated many observational and
scientific innovations that are prominently featured on the Haystack
history wall and well represented in heavily cited literature.  For
example, he worked closely with the late MIchael Buonsanto on an innovative
10-position radar experiment that yielded arguably the first quantitative
determination of gradient terms in the heart of ionospheric physics
equations - namely the continuity equation.  John also created an
production level uniform-grid and model friendly Millstone Hill vertical
electron density for each radar experiment,  targeted at easy ingestion for
theoretical and empirical studies.

John's fingerprints and deep insights in geospace remote sensing by radar
also led to a flexible and productive implementation of Markku Lehtinen's
alternating codes as a revolution for improved ionospheric radar data.  He
created pioneering software radar systems, initially using RPC
infrastructures in the VME-based MIDAS-1 control stack and later in
completely Unix workstation based systems (MIDAS-W).  These efforts were
interleaved with early bistatic radar control architectures in
international collaborations with the Canadian Algonquin radio telescope
(MIDAS-C).  During this work, John extensively collaborated with many
groups across the globe, including the former Soviet Union, and created
advanced EISCAT mainland radar control innovations with Tony van Eyken,
then the EISCAT director.  His creation of the OASIS package for full
profile ionospheric radar, which uses B-splines to optimally derive the
complete ionospheric altitude profile at once, was documented in a well
cited paper in 1990 and is still being cited in the radar community.

John was the creator of the influential Madrigal database system at
Haystack beginning in 1980.  Initially designed as an internal tool to
store and retrieve incoherent scatter radar data for use in Haystack
science studies, Madrigal has grown far beyond this original purpose over
the decades.  Today Madrigal is operated at Haystack by the NSF Millstone
Hill Geospace Facility as the world's largest ground-based repository and
permanent archive of upper atmosphere remote sensing data of all kinds,
with truly international reach across all of space science. In this role,
Madrigal has enabled many thousands of observational science papers in
upper atmosphere studies.

In ionosphere science, John's scientific output produced many unique
long-term trend studies that revealed climatological variations over
decades and solar cycles through use of the extensive worldwide incoherent
scatter radar observational record.  In the process, John was responsible
for digitally assembling the entire available historical radar catalog for
flexible community use - including painstaking data recreation of crucial
legacy observations from radar experiments existing only as scanned
printouts on microfiche!

John was very active in the geospace community, including serving on the
CEDAR Science Steering Committee, the EISCAT scientific advisory committee,
and as a long-standing member of both the American Geophysical Union (AGU)
and the International Union of Radio Science (URSI). John also served as an
energetic research mentor beginning in 1994 for dozens of undergraduate
students in Haystack's NSF Research Experiences for Undergraduates program.

After retirement from MIT, John traveled extensively across the world and
enjoyed playing tennis, running and spending time with his family. John is
survived by his partner Barbara Lorenc, brother Dennis, daughters Amanda
and Melissa and their spouses and five grandchildren. John was predeceased
by his wife, Barbara Holt. His colleagues and friends at Haystack and
throughout the scientific community will miss his presence deeply.

-- Phil Erickson and the Geospace research group at MIT Haystack Observatory

-----
Philip Erickson (he/him), Ph.D.
Director
MIT Haystack Observatory
Westford, MA  01886  USA

email: pje at mit.edu <pje at haystack.mit.edu>  [NOTE NEW PREFERRED ADDRESS]
WWW: http://www.haystack.mit.edu
voice: +1 617 715 5769
fax:   +1 617 715 5590
Public key: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x54878872
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