August 2026: Dr. Joseph (Joe) Turk
2010 – current: Joint Institute for Regional Earth System Science & Engineering (JIFRESSE), Univ. of California Los Angeles.
2009-2025: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA.
1994- 2009: Marine Meteorology Division, Naval Research Laboratory, Monterey, CA.
1984-1986: Cellular Communications Group, Motorola, Inc., Schaumburg, IL.
Background
- Where are you from, where did you receive your education, and what in?
I am originally from the iron range of Minnesota, but my parents soon moved to the Upper Peninsula of Michigan. I graduated from high school in a small town called Iron Mountain, located on the border with Wisconsin, and which had an excellent school system. My college degrees are in electrical engineering, from Michigan Technological University (MTU), and later from Colorado State University (CSU).
- What was your introduction to precipitation science?
Starting at a young age I wondered how electricity, antennas, and radio worked; the connection to weather came later. After graduation from MTU in 1982 I was about to accept a position with one of the large aerospace companies in the Boston area, but my roommate at the time encouraged me to look into graduate school for 2 more years and earn a MS degree. I’d had an antennas course with a professor named Jim Rogers who I have long lost contact with, but he was the one who introduced me to remote sensing and its use for physical sciences, and I stuck around. That summer Rogers involved me with fieldwork in the Upper Michigan forests setting up ELF (extremely low frequency) magnetotelluric measurements (electromagnetic fields that are transmitted from far away sources such as lightning storms, and whose local intensity and polarization state is related to the complex permittivity of the deep underlying rock structure). At these frequencies, to meet Nyquist sampling implied several days of continuous data collection at each site. The resulting geophysical maps were used by the Navy when they built long ELF antenna dipoles a few years later, enabling communication with submersed submarines. I used these data for my M.S. degree topic and taught undergraduate level circuit theory classes.
After graduation I worked for Motorola, Inc. in the Chicago area. In the mid-80s, the cellular mobile telephone industry was getting underway. Antitrust legislation had recently broken the Bell System telephone monopoly into the so-called “baby bells” and allowed local providers to provide cellular service. Motorola provided much of the equipment and calls were encoded and multiplexed using analog techniques. After a few years in various technical roles the company assigned me to the service repair training group. I’d often fly out on short notice to teach service classes to technicians at different providers. I noticed again that I liked to teach and felt good when others grasped concepts that I’d explain in simpler terms. The company was finding it challenging to compete cost- and manufacturing-wise with cellular products manufactured in Japan. I didn’t envision a meaningful long-term future and remembered how much I enjoyed teaching and data analysis.
I’d known someone at MTU who had graduated from CSU and mentioned the radar projects of a professor named Dr. V.N. Bringi (the fact that the bicycling in Colorado was spectacular was also a big push). In 1986 Bringi had been awarded a large grant from the Army Research Office. I was super fortunate; he offered a graduate research assistant fellowship available to study precipitation measurement with dual-polarimetric radar, which was in its formative years. While traditional radar concepts were familiar to me, I had never been exposed to use of radar for weather. This was when the NCAR CP-2 dual-polarized radar was being deployed to large field campaigns. Bringi’s postdoc, Dr. J. Vivekanandan (now NCAR senior scientist) largely served as my advisor.
At the time there were only a few people using ground-based polarimetric radar to forward-simulate multi-channel passive MW observations for the Tropical Rainfall Measuring Mission (TRMM), which had recently been proposed. CSU had coordinated CP-2 dual-polarization scans with the Advanced Microwave Precipitation Radiometer (AMPR) airborne passive microwave radiometer built by Marshall Space Flight Center (MSFC). Around 1990, Special Sensor Microwave Imager (SSMI) data became publicly available. These simulations with SSMI and AMPR data showed the sensitivity to hydrometeor vertical structure across the different passive MW channels, at different resolutions. While others previously demonstrated the precipitation-sensing capabilities of the SSMI 85 GHz channels, AMPR helped to demonstrate the need for 10 GHz channels later included with TRMM.
- Was there a person, project or moment early on that helped to shape the direction of your career?
Growing up in a remote area, we had only one AM radio station which played the hits of the day later in the evening, and I was curious why their transmitted power was reduced around sunset. Sometimes at night I’d walk up the hill behind our house where the station antenna tower was located, where I would pick up the more powerful stations from Chicago and beyond. This was also an era where citizen’s band radio was popular, and a nearby high school friend had one. These experiences led to learning about propagation and the impact of the Earth’s ionosphere and tropospheric conditions. If I had to name one person it would be my high school physics teacher, Richard Debelak. The way that I explain math and physics concepts was directly inherited from his teaching style and methods. He was always in his office by 7AM if anyone had questions. He also had a role in seeing that I received an engineering scholarship upon graduation.
Scientific Journey
- What topics in precipitation science have you tackled throughout your career?
My career has largely been as a “data scientist”. In general, the topics have all been associated in one way or another with the use of satellite-based passive and active MW observations for weather, particularly to precipitation. Along the way there’s been different topics which I can describe below.
- Which institutions/places were important in your research journey?
Each place along the way provided a different type of opportunity and I am grateful for all. NRL-Monterey provided early opportunities to develop interactions within Navy, NOAA, NASA, and international satellite providers and programs. During this time, I also became involved with the AMS Satellite Meteorology Committee and the International Precipitation Working Group (IPWG), a specialized working group of the Coordination Group for Meteorological Satellites (CGMS). I am grateful for support from Navy, NASA and JAXA programs.
- How did your research focus change over time, and why?
The focus was influenced by where I was working at the time, the types of funding opportunities, and meeting good colleagues with whom to propose joint efforts. Like many, I worked in multiple areas at the same time. Along the way there were many failures, assignments that I didn’t feel like I delivered on, expectations that needed to be rolled back. Coming from an engineering background, I looked for ways practical, useful. I’ll share some experiences.In the mid-90s, the new Geostationary Operational Earth Satellite (GOES-8) introduced a new direct-broadcast telemetry which greatly simplified ground processing, and space-based precipitation radar became a reality with TRMM. The processing center at Goddard Space Flight Center (GSFC) made near real-time TRMM data available. Yet much of these data were not making to the users in a timely fashion. Our NRL-Monterey group sought a way to marry the collection of geostationary and MW observations to the tropical meteorology community, including operational centers such as the Navy/Air Force Joint Typhoon Warning Center (JTWC), the Fleet Numerical Meteorology and Oceanography Center (FNMOC), and NOAA’s Hurricane Research Division (HRD). These and other users relied upon TRMM and other passive MW, geostationary and scatterometer imagery disseminated in near real-time via the popular NRL-Monterey “TC-Web”, and the “NRL-Blend” was an early self-calibrating merged MW and geostationary IR satellite precipitation product. After 9/11, NRL-Monterey devised a similar means of dissemination of near real-time MODIS-derived atmospheric products, which were utilized for weather and aerosol forecasts in the Persian Gulf area.
With GPM in 2014, there was a need to improve the quality of the precipitation products over a wider variety of non-water Earth surfaces than TRMM sampled. The larger and more variable microwave surface emissivity controls the extent to which precipitation can be detected and quantified from passive MW observations. Our research demonstrated how the leading principal components of the surface emissivity vector were related to a few key surface geophysical factors. We devised a simple technique to estimate these components from the passive MW observations, and how they change as precipitation develops. The methodology has been adopted by some product developers for discriminating precipitation-impacted passive MW observations.
The radars onboard TRMM and GPM have limited sensitivity to light and frozen precipitation. Addressing this known shortcoming became more urgent after GPM and its expanded latitude coverage. From TRMM and GPM, it was possible to build multi-wavelength radar and multi-channel radiometer observations from near coincident observations between GPM and other low Earth orbiting satellites, including the short-wavelength CloudSat cloud radar. The resulting dataset has been useful to the wider user community for validation, to address GPM algorithm shortcomings, and for AI training purposes. This dataset is being continued with EarthCARE.
Water vapor is the “fuel” for convection and heavy precipitation. One type of climate model diagnostic involves the ability of a model to replicate observed water vapor-precipitation relationships. However, the water vapor structure deep inside of heavy precipitation is challenging to measure from current passive or active MW satellite observations. Around 2010 I was introduced to Global Navigation Satellite System (GNSS) radio occultation technology through JPL and Spanish colleagues. Together we proposed the polarimetric radio occultation (PRO) concept, which provides a joint measurement of water vapor, temperature and precipitation structure. Spain built the first PRO receiver and deployed in 2018 as a secondary payload on their radar satellite. Analysis using GPM data proved that the concept worked. Recently PRO capabilities have been included in commercial GNSS systems, and these data are being assessed for weather forecast model applications.
Around 2010 experiment modules built by JAXA and ESA for the International Space Station (ISS) were opening to Earth observations. These provided short-term opportunities to host a payload or test an observational strategy. In 2014 the JPL RapidScat scatterometer was installed on the Columbus module. RapidScat provided local time varying measurements (like GPM) of ocean surface wind vectors but only operated for two years. Analysis revealed diurnal and sub-diurnal modes of zonal and meridional ocean surface wind variability across the tropical convergence zone, where the heaviest precipitation is concentrated. In 2022 the JPL Compact Ocean Wind Vector Radiometer (COWVR) and Temporal Experiment for Storms and Tropical Systems (TEMPEST) duo began operations from the JEMS module, enabling some observational capacity for connecting ocean-atmosphere interactions. Our JPL group used the collection of these data to estimate precipitation height relative to the freezing level (a proxy for convection strength) and linked this with evidence of nearby convergence or divergence signatures in the ocean surface wind field.
Evolution of Precipitation Science
- How has your area of precipitation science evolved throughout your career?
While the algorithms and techniques that create merged precipitation datasets have evolved, the biggest evolution in the data has occurred from their broader application outside of the scientific community. Precipitation is complementary to other types of Earth environmental observations and needs to be specified for applications where precipitation is an influencing factor. Readily accessible data servers, providing sustained near real-time updating global products have made it much easier for users of all skill levels to access the necessary precipitation data.
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What major advances do you believe have most advanced the field (e.g., observations, theory, modeling, radar/satellite, computation, AI/ML, etc.)?
I’m certainly no expert in many of these. It’s obvious that AI/ML methods are already transforming ways in which we design, build and train inversion algorithms. And to merge/combine various ground, satellite and model observations for unified global precipitation data products. But we still need the best satellite systems and sustained global satellite observations for training these techniques. The continuing technology development and miniaturization of small/cube-sized satellite platforms, passive/active MW sensors, geostationary imaging, GNSS and other unconventional observations on ground and space will alter the makeup of the global satellite precipitation constellation in years to come.
For weather forecasting, steady progress is being made in ways assimilate precipitation-impacted observations into forecast models, all the while adapting to a diverse and changing constellation of observation types. At programmatic levels, there has been a greater realization of how and where precipitation measurement fits in amongst other space-based measurements of the Earth’s hydrosphere.
For low-Earth orbiting satellite data, there has been a much greater importance placed upon the needs of the applications community. There is more priority for disseminating low-latency data to the multitude of users that depend upon short-term forecast and other situation-awareness products.
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What future advancements/directions do you foresee in precipitation science?
The role of commercial satellite companies to provide Earth observations from technology-ready, low-cost sensors will continue to grow. The commercial providers can build and deploy these systems faster. The challenge for precipitation science will be to assure that licensing agreements for commercially provided data are written to assure timely access to the best quality data.
The space agencies have and continue to collect more Earth observations, the satellite data record continues to expand, yet much of the information remains underutilized. AI provides a means to make discoveries about patterns in these data much faster than before. While today’s global satellite precipitation data products provide 2-D maps, future products will also provide information on its vertical structure.
Nowadays it’s taken for granted with the overlapping TRMM and GPM eras, but the availability of an inclined-orbit core spacecraft with joint precipitation radar and high-quality MW radiometer capabilities is fundamental to how constellation-based precipitation products are created. I say this now since it’s important to assure that this capability is sustained in a future post-GPM era.
As a caution, there’s a worrisome tendency to assume that “more satellites=better products”. Mass, size and power constraints of current small satellites leave off the lower frequency, constant Earth incidence MW channels preferred for quantitative precipitation measurement. If left unaddressed, this will impact the quality of the resultant global satellite precipitation products. These sensors also sustain the long record of ocean surface winds, sea ice, and column water vapor.
Reflections and advice
- What is the proudest moment of your career?
Although I never had a formal teaching role, the proudest moments come my roles in furthering the well-being of students and early-career individuals that I had the opportunity to sponsor and advise. Whenever I attend conferences or meetings, I always make a point to introduce myself to people that I don’t know, first-timers, students, international attendees, etc.
- What is your favorite research paper/project that you produced?
It would be a side project in the mid-2000s between NRL-Monterey and Google with colleagues Steve Miller (now CSU faculty) and Jeff Hawkins (now retired). At NRL-Monterey we had access to global, full-resolution, real-time geostationary satellite imaging data. Steve and I developed a global cloud product that merged various channels from all the imagers. At that time, Google Earth had recently been released and there was quite a bit of activity directed towards visualization of geoscience data within virtual globes using KML. Steve had come up with a clever way to activate the transparency layer in such a way that a realistic-looking global cloud depiction could be overlaid upon other Google Earth layers. We wrote a paper on this and presented it at AGU, and the Google Earth team approached us with interest. Legal staff at NRL-Stennis and Google worked out the details. We interfaced with the visualization team at Google who added an auto-updating near real-time global cloud layer option in Google Earth. I remember inviting the founder of Google Earth, Michael Jones, down from Sunnyvale to give a seminar at NRL-Monterey.
- Who has inspired you most throughout your career?
The most inspiration came every day from my wife, Ida. In addition to admiring her unique skills as a technical recruiter, she witnessed the multitude of organizational activities that I was involved with both inside and outside official job duties, and she understood and supported me.
Throughout my career I was inspired by the longstanding international cooperation between NASA and JAXA in satellite precipitation measurement programs. Of course, Bringi at CSU, brilliant, and gentle, kind, humble man. I was honored to speak at his memorial in 2025. Jeff Hawkins, who hired me at NRL-Monterey, a visionary on recognizing the need for delivery of low-latency microwave satellite data to weather centers and forecasters. Estel Cardellach at CSIC/ICE in Barcelona, Vincenzo Levizzani and Alberto Mugani at ISAC in Italy, and Johannes Schmetz at EUMETSAT for their leadership of European satellite projects, to name a few. I’m proud of my leadership roles in IPWG and CGMS, these were very meaningful. I’m indebted to Vincenzo Levizzani and Ralph Ferraro for supporting me in these roles.
- What advice would you give to students and early-career scientists entering precipitation science today?
To the degree that you are able, find a position where you are surrounded with good people, which may not necessarily be on the specific topic that you want to work on. Of course, this is not always possible, and you will have limited control. Be open to establishing your network of contacts and collaborations, but don’t become too comfortable in them. It’s important to be recognized for a specialty area but also step away and try other things. Be consistent, acknowledge your peers. Ultimately, people remember those who move with unselfish commitment.
Sustainment of global satellite precipitation products is a constant ongoing process. It’s important to sustain international precipitation workshops such as IPC and IPWG, the latter being a venue where the precipitation measurement community can voice recommendations to the international CGMS member agencies.
Within the precipitation sciences, you will be exposed to many disciplines, technologies, datasets, quantitative analysis methods, and by its very nature the field is very international. In other words, you will build an expansive and diverse toolkit. Be open to using this to explore jobs and career opportunities you didn’t envision years prior but are now interesting to you.
Of course, our lives are products of the factors that surround us. Employment opportunities may be constrained by family or health matters, location, housing, and income levels, which limits where one can live and what one is able to do. Find a work-life balance that works for your situation.
- If you were starting your career today, what would you focus on?
Looking about the state of the Earth today, I would say perhaps in an area of health care or a medical field where skills will always be needed, taking care of people, well-being of others. If I were to pursue the environmental sciences, I’d be interested in having a role in assuring adequate freshwater availability, water quality, water usage. These will always involve debate and compromise since country and state lines don’t align with watershed boundaries and rainfall patterns.
- Outside of science, what hobbies or activities have been important to you?
I’ve been fortunate to live near areas of the western US with ample outdoor opportunities for the mountains and deserts and have met some fine people from all around the world. I was fortunate to have the type of work that enabled travel to many different states and countries. One’s external activities will arise inspiration in ways that you least expect. The works created by musicians, athletes, tradespeople, volunteers, writers, educators have inspired me in different ways. For example, oftentimes I’d get technical ideas during concerts, watching each musician play their instrument, making it all work together in a group setting. Creativity unfolding in one way and unfolding in another.
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