INTRODUCTION
The Sensor Science Division (SSD) of the PML conducts an extremely broad set of technical activities. The division creates and produces devices and articles as primary and secondary standards for dissemination, creates standards, and does fundamental science in a diverse set of technical fields. These fields include optical, temperature, and pressure measurement, as well as imaging and flow. Size scales range from a few atom widths to many meters and system complexity ranges from photonic devices to satellites and smokestacks. The division comprises a division office (6 staff and 3 associates), overseeing the work of six groups: Thermodynamic Metrology (16 staff and 3 associates), Fluid Metrology (10 staff and 1 associate), Optical Radiation (16 staff and 3 associates), Infrared Technology (10 staff and 9 associates), Laser Applications (9 staff and 1 associate), and Ultraviolet Radiation (10 staff and 1 associate). However, the review of the division was conducted along the lines of programs, as carried out in various facilities. The high degree of collaboration within the division results in the fact that a given program is almost always supported by staff from more than one group; however, it was not always clear which groups, and how many staff from each, supported each program. The panel therefore conducted its assessment on the basis of the facilities it had the opportunity to observe, and the thematically coherent programs conducted within them, rather than attempting to assess the groups themselves.
ASSESSMENT OF TECHNICAL PROGRAMS
Vision Science Laboratory
The research work presented in the vision science laboratory is mature, and its results are ready to be introduced as a worldwide standard. The team working in this area is exploring solid-state lighting from a psychological point of view. The results of this study are important because they will impact the replacement rate of incandescent lighting. Lighting comprises a significant fraction of the nation’s total electricity usage, and solid-state lighting has the potential to reduce electricity usage for lighting by a factor of 10 or more. One big difference between incandescent and solid-state lighting is the ability to control the color of the light. Currently, solid-state lighting is specified by the light output (lumens) and the color temperature. The vision science team has added a third factor, chromaticity or tint, and has found that people prefer a pinkish tint. The desired tint depends to some extent on the cultural background of the subject. This finding is likely to broaden the appeal of solid-state lighting, accelerating the transition, saving energy, and reducing CO2 emissions.
Optical Properties of Materials and Spectroradiometry
The research in the areas of optical properties of materials and spectroradiometry appears to involve excellent personnel and equipment with accuracy over a prodigious spectral range from 4 nm to 100 µm. This team conducts a significant portion of the division’s measurements for customers and has a wide and deep outreach program, participating in standards organizations, training personnel from other national measurement laboratories (NMLs), conducting short courses, performing phantom development, and generating publications.
The reflection measurements are being automated to save customers time and money and to reduce the workload of highly trained personnel, allowing them to pursue more creative activities.
The reflection measurements were not conducted or stored in a clean and dry area. This could be acceptable if it were an experimental setup or if the measurements did not require the accuracy of samples free of a small amount of dust.
Photonic Sensors and Standards
An overarching theme at the division is the development and deployment of NIST-traceable measurements and standards that are reliably produced in low size, weight, and power (low-SWaP); low-cost (low enough to enable broad customer deployment, or even embedded applications), integrated packages producing one or more measurements. At an institutional level, this initiative is known as NIST-on-a-Chip, where the overall goal is to develop and deploy SI-traceable measurements and physical standards that are deployed in the customer’s environment. The desired attributes are usability (small size, low power, rugged, easily integrated and operated); flexibility (broad range of SI-traceable standards, possibly including a few to many measurements from an single small and affordable package); and manufacturable (low cost for broad deployment or acceptable cost for high-value applications). Within the SSD, there are numerous examples of this theme in development. An example of particular significance is the development of a dynamic pressure standard based on wavelength modulation spectroscopy. Two significant aspects of this project are these: (1) dynamic pressure measurements are particularly difficult and inaccurate using current approaches, most of which are designed to measure static, or slowly varying pressures, so that some important, highly dynamic situations, such as shocks, are measured with significant inaccuracy; and (2) there are many extremely important application areas that require relatively inexpensive, broadly deployed (or especially embedded) measurement systems. A prominent example with both high economic and policy impact is the phenomenon of traumatic brain injury occurring in sports and in military combat. The potential for sensors in this context is recognized by the PML, and that application is guiding some aspects of the current program. As the research progresses, it will be important to assure that measurement of acceleration and “jerk “(the third derivative of distance with respect to time) is being considered, with the objective of developing an integrated accelerometer/dynamic pressure sensor.
Low-Background Infrared Facility
The low-background infrared (LBIR) facility specializes in low-power infrared measurements with wavelengths from 2 to 30 µm, and it does so at a physical scale sufficient to test actual sensors used in astrophysics and missile defense. The LBIR receives significant support from the Missile Defense Agency (MDA) and is used extensively by some of the MDA’s major contractors. The NIST traceability of radiometric measurements is one of the singularly defensible (technically) aspects of MDA’s programs of record, which have undergone significant programmatic upheavals.
The LBIR’s strong customer focus leads to several issues and uncertainties concerning its future. The underlying research program, focusing on high-sensitivity electrical substitution radiometers, solid-
state trap detectors, fluid bath cryogenic vacuum blackbody sources, and carbon nanotube sources and detectors, does not seem as closely coupled to customer needs; evidence of such coupling was not presented during the assessment. The LBIR needs to ensure that one of the MDA contractors, Johns Hopkins University (JHU) Applied Physics Laboratory, is not essentially duplicating the NIST capability. The extreme politicization of missile defense over the past 6 years makes the MDA program highly unstable and has led in the recent past to significant management and programmatic upheavals. The LBIR needs to undertake scenario-based planning to seek a broader customer base, aligning the research program to the needs of other customers, such as the National Aeronautics and Space Administration (NASA) and to minimize disruption that might occur with a significant, unpredictable change in MDA support.
SIRCUS/Satellite Sensor Calibration/Ocean Color/Space Weather
This program and its primary facility, the spectral irradiance and radiance responsivity calibrations using uniform sources (SIRCUS) facility, underpin optical metrology in terms of power, irradiance, and radiance for a broad range of important measurement systems with high operational and scientific significance, such as weather satellites, land and ocean color sensing, stratospheric aerosols, Earth’s radiation budget, and corresponding ground truth artifacts. The range of customers is impressive: NASA, NOAA, the National Geospatial-Intelligence Agency (NGA), and the Department of Defense (DoD).
Given the ever-increasing importance of hyperspectral measurements and imaging, the increasing emphasis of SIRCUS on calibration methods and standards for such systems is admirable.
One possible caution concerns the increasing emphasis on lower-cost, lower-SWaP sensors for future satellite systems, following the National Polar-orbiting Operational Environmental Satellite System (NPOESS) programmatic debacle, and the later cancellation of the DoD-focused Defense Weather Satellite System (DWSS). The SIRCUS team could explore (and perhaps partner in development of smaller radiometric sensor systems for satellites. It is possible that the upcoming NASA preaerosol, clouds, and ocean ecosystem (PACE) mission, if awarded competitively, could provide an opportunity for disruptive developments in radiometers that would effectively displace the Visible Infrared Imaging Radiometer Suite (VIIRS). At a minimum, the division could prepare to calibrate much smaller radiometers for its customers.
Pressure and Vacuum Measurement Program
These efforts are important and will particularly impact semiconductor manufacturing, where molecular-level control of pure environments is critical. Photonics measurement will replace, among other measurement methods, a 3-m mercury column and will enable a route to faster measurement that can be more easily deployed to a field environment by means of handheld devices usable at room temperature. This effort to integrate the standard and the sensor is consistent with the priorities of NIST-on-a-Chip. There are also significant efforts to automate calibration and testing to improve service for customers, including reduced turnaround time and lower cost.
Members of the team are amongst the best in the world in their activities to reinvent pressure measurement, having won several awards within their communities, published papers, and pursued numerous patents. Overall, the efforts of this program are commendable and on a good trajectory.
Fluid and Flow Metrology
This program has provided best-in-the-world capability to realize flow measurement over 11 decades for gas flow and 5 decades for liquid flow. The team has won several awards and honors recently for its efforts in these areas. A notable effort is the characterization of hydrogen flowmeters for high-pressure refueling of hydrogen-powered vehicles with reduced uncertainty and rapid response times. A portable field test standard has been developed for use at refueling stations. This work is impressive and important as the world seeks alternatives to fossil fuels. Other flow metrology efforts include use of microwave resonances to measure large volumes and efforts to develop methods for measuring microscale flows.
Acknowledging the challenge of quantifying small-scale flows, it would be worthwhile for the team to continue developing other noninvasive and in-line ways to determine microflows that can be readily integrated into devices. The development of measurement methods for multiphase flows is also worthwhile. These are challenging areas that are becoming increasingly important with the growth and use of hydraulic fracturing methods.
Smokestack Simulator Laboratory
As the world places a higher cost on emissions of CO2 from coal-burning power plants, the need for more accurate measurement of these emissions increases. In response to this need, a new, first-in the-world, 1:10 scale model of a swirling smokestack is being built and tested. The challenges lie in the very rapid, turbulent, 3D, swirling nature of flows in smokestacks, and in the need to accurately measure transport of CO2 within this type of flow, in very harsh environments. The PML is at the forefront in developing tools and calibrations to address these needs, emphasizing accurate, systematic, and appropriate use of long-wavelength acoustic flowmeters. Though still in early stages, these efforts are excellent and hold significant promise for aiding national efforts to limit environmental release of greenhouse gases.
Synchrotron Ultraviolet Radiation Facility
The Synchrotron Ultraviolet Radiation Facility (SURF III) is a nationally unique facility providing NIST traceability for (most) solar-observing and space sensors operating in the UV and extreme UV part of the spectrum. These instruments underpin the current understanding of solar variability and its potential contribution to global climate change. SURF III also underpins the current understanding of parts of space weather, and its potential impact on critical national and international infrastructure in space. Its customer set includes NASA, NOAA, and the DoD. The facility is under active development to provide NIST-traceable irradiance measurements from 2 nm to 500 nm with less than 1 percent absolute uncertainty (current capability is 4 to 400 nm). The facility also calibrates approximately 25 photodiodes per year to disseminate the radiometric scale over SURF’s spectral regime.
The quality of the work done at SURF supports broad international collaboration, despite the relative decrepitude of the radiation physics building (building 245). Notwithstanding the challenges of operating in this building, this was the one facility within the SSD that was not meeting the standards for neatness and order that characterized the rest of the facilities visited; this building needs attention.
Conclusion
The division’s general strategy of moving metrology from pristine laboratory contexts to more complicated real-world environments associated with applications is commendable. The division appears
well coupled to the communities it serves and strives to solve their problems with the goal of better, safer, and more useful products. The emphasis on low-cost, portable, photonic, and potentially embedded standards is particularly relevant and consistent with the theme NIST-on-a-Chip.
While the overarching strategy was well articulated, the division did not describe plans for some of the projects, particularly those that are funded externally; those working on internally funded initiatives seemed to have more concrete plans.
PORTFOLIO OF SCIENTIFIC EXPERTISE
The SSD is a large division created several years ago by combining a number of disparate activities with multiple areas of expertise and capabilities. The division is now synergistically very productive; this is a testament to good management. It is a division of outstanding and very capable people who cover a large spectrum of technology and science.
Despite the impressive breadth of technical areas, the SSD appears to be leaders in all their activities, in measurement and, in many cases, the underlying science. They participate in and lead national and international standards committees in their fields of interest, and they have generated numerous publications and patents. Many of the world’s other leading standards laboratories send staff to be trained at this division and ask for their staff to visit and transfer technology. The division is asked for help by many leading organizations with exacting requirements for measurement accuracy such as NASA, DOE, and DoD laboratories.
The staff seemed very knowledgeable in the domains related to their activities, in terms of their specific work and in terms of worldwide scientific and technological developments. Many of the staff are leaders in their fields. There is a general expectation of excellence and objectivity and very good alignment with the public service mission of NIST. The division conducts a large fraction of the NIST calibrations and dissemination of secondary standards, but staff expressed little objection to doing routine measurements or supplying multiple samples. In fact, members of the division expressed pride in the number of samples they produced and expressed desire to find ways to make them cheaper and to find ways to automate the measurements for faster and better service.
The division did not describe a strategy for maintaining its spectrum of excellence and diversity (age, gender, ethnicity, and expertise) of human capital to maintain the division’s preeminence over the long term. Flat funding exacerbates this problem, but addressing the problem is very important and worthy of effort and a definitive plan. In particular, the presumption that a practical solution will be achieved by a likely delay in senior staff retirement is neither constructive nor forward-looking, even if that pattern is based on experience. Very few people maintain high creativity for decades, and simply delimiting the desired spectrum of staff attributes by length of experience seems to fall short of desired management principles in an institution with a critical mission.
ADEQUACY OF FACILITIES, EQUIPMENT, AND HUMAN RESOURCES
The division appears to have excellent facilities, and the work spaces are generally well maintained. The one exception was the SURF area. Division management acknowledged that this building needs a refurbishment, but much can be done to improve the situation in the short term with a clean-up and attention to making the area safer.
Quality Management System in the Sensor Science Division
Support of the QMS in the Sensor Science Division is viewed as supportive of the overall PML mission, and not a system populated by checkers. The PML is to be congratulated on this approach. The
NIST PML mission of maintaining and improving the U.S. (and, through consultative committees, the international) SI system of physical measurements requires exacting standards and the implementation of quality control throughout its divisions. The standing of the PML as gauged by international comparisons, customer feedback, and interaction with stakeholders speaks to the effectiveness of the overall quality management system (QMS). It appears that the QMS is implemented in a way that maximizes efficiency and minimizes staff requirements. In other contexts, including those of the International Organization for Standardization (ISO) and national standard regimes, such as AS9100, quality assurance is envisioned as requiring a completely parallel staff system, which is frequently viewed by customer-facing staff as redundant, threatening, and contributing to overhead. The PML apparently implements its QMS using staff who themselves have customer-facing and customer-supporting responsibilities This leads to a constructive team dynamic and endows the staff implementing the QMS with moral authority when inevitable problems arise. QMS in the Sensor Science Division is viewed as supportive of the PML mission and not a system populated by checkers. The PML is to be congratulated on this approach.
