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Assessing Bias in Lunar Irradiance Model Outputs Using Nighttime Aerosol Optical Depth Retrievals
Get PDFTypical lunar calibration applications utilize spectral irradiance for comparing sensors’ lunar measurements against a reference. Because the Moon’s brightness continuously changes with time and the sensor location, reference lunar irradiance values are generated for the particular Sun-Moon-viewer geometry of the instrument’s observations by computing a numerical model. Nighttime aerosol optical depth (AOD) retrievals using ground-based photometer measurements and the Langley method require accounting for changes in the Moon’s brightness over the Langley data collection period, typically 1-2 hours. Models used for lunar calibration provide the exo-atmospheric irradiances needed for the Langley analyses. The success of nighttime AOD retrievals is indicated by continuity with daytime AOD measurements. To achieve this day-night consistency, scale offsets have been found necessary to be applied to the outputs of current lunar irradiance models.
A recent AOD measurement campaign conducted at Izana observatory (28.3 deg N, 16.5 deg W, 2401 m.a.s.l.) collected lunar measurements with a Precision Filter Radiometer (PFR) developed at PMOD and calibrated at the TULIP facility at PTB. Using the USGS ROLO model to predict the nightly relative lunar irradiance variations, the Langley analyses and AOD retrievals have produced top-of-atmosphere lunar irradiance measurements with expanded relative uncertainty under 0.5%. These measurements provide reliable, quantitative evaluations of the uncertainty and bias in the outputs of ROLO and other lunar irradiance models. They will be used guide advanced lunar modeling toward higher accuracy and an improved lunar calibration reference
Assessment of PACE OCI Linearity Prelaunch and On-orbit
Get PDFThe Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, recently launched in February of 2024, has a payload of two polarimeters and the Ocean Color Instrument (OCI). OCI is the next generation sensor for ocean color science from low Earth orbit, drawing heritage from sensors such as MODIS, SeaWiFs, and VIIRS, but with increased spectral coverage and improved accuracy. OCI is a grating spectrometer with hyperspectral coverage from the ultraviolet (about 315 nm) to near-infrared (about 895 nm), with additional filtered channels in the short-wave infrared (940 nm – 2260 nm). In order to maintain the high levels of accuracy demanded by the science community, the sensor calibration is monitored on-orbit. The hyperspectral channels on OCI have a special operating mode in which images of varying integrations times can be measured in a single scan line. This mode in conjunction with solar observations via a dim diffuser (with ~2-3 % reflectance) allows OCI to collect images covering the dynamic range in a single scan. This data can then be used to assess the linearity of the system, comparing to measurements made prior to launch, assess the stability of the system, and possibly update the calibration algorithm. Linearity measurements are made every month and the results are trended over the mission
Self-Calibration of Photodiodes using the Dual-Mode Method
Get PDFIn 2014, White et al suggested to combine the measurement principle of the two primary standards for optical power measurements [1]; the cryogenic radiometer and the predictable quantum efficient detector (PQED). The result was the dual mode operated induced junction photodiode, for which the internal losses of the diode are estimated by comparing the two modes of operation, i.e. electrical substitution and photocurrent measurements. During the electrical substitution measurements, the optical power is found through the temperature at the diode, which is measured using a thermistor located close to the diode. The diode is cycled between electrical heating (forward bias) where the power is precisely defined, and optical heating (using the diode as a passive absorbing element). Since the initial demonstration, significant improvements in the room temperature dual mode measurements have been achieved, bringing the uncertainties close to that given by cryogenic radiometer. [2]
The measurement system presented in this work consists of an induced junction photodiode which is connected to a heat sink through a weak heat link. The module is placed in a vacuum chamber, and a laser beam (HeNe laser with a wavelength of 633 nm) is directed at the diode through an Ar-coated window. Building on the system from ref [2], we present an improved measurement setup where the electrical coupling and grounding considerations have been improved. This has resulted in more accurate estimates of internal losses over a broader dynamic range. The internal losses are position dependent, with an average of 0.00% ± 0.04% for optical power as low as 366 μW, compared to 0.08% ± 0.04% at 500 μW, as reported in [2]. The uncertainties are limited by the thermal non-equivalence between electrical and optical heating.
In this work we also propose an improved temperature drift compensation, resulting in a reduction of uncertainties by a factor of four compared to previously reported results [2]. In addition, refinements made in the data analysis provide a clearer and more transparent interpretation, facilitating a better understanding of system variability. These refinements have resulted in a robust methodology for estimating uncertainties which corresponds well with observed variation in the measurements. We also demonstrate the importance of propagating absolute uncertainties, as the observed standard deviation in the internal quantum deficiency depends on the relative position of optical power related to the electrical power even if the noise level is constant.
This work demonstrates increased absolute radiometric measurement capability of room temperature dual mode detectors with uncertainties as low as 0.04 % limited by the heat equivalence of the dual mode assembly design. Work is ongoing to design and produce dual mode modules with better heat equivalence. The dual mode method represent a robust absolute radiometric measurement of any type of photodiodes, not just limited to PQEDs, with the potential to bring self-calibration directly into instruments and remote locations over a wide spectral range.
References: [1] White, M. et al. (2014). Metrologia, 51(6), S245. [2] Ulset, M. et al. (2022). Metrologia, 59(3), 035008. Tuesday, June 11, 202
GLAMR Calibration as an Absolute Radiometric Calibration Approach
Get PDFThe pursuit of highly accurate remote sensing instrumentation has driven the need for an improved, SI-traceable radiometric calibration (RadCal) methodology. A notable example of this necessity is the calibration of the Hyperspectral Imager for Climate Science (HySICS) instrument under the CLARREO pathfinder project, with a stringent calibration requirement of 0.3% (k=1), which is much lower than the existing state-of-the-art instruments. Detector-based absolute RadCal in the solar reflective region has become possible with the implementation of the tunable laser source. One such system is the GLAMR system developed at NASA Goddard that can scan the spectral range of 340-2500 nm. RadCal using GLAMR as the light source has been performed on several major operational instruments, often as part of their spectral characterization to measure the relative spectral response (RSR). Absolute detector responsivities (ASRs) are measured during the process, leading to simultaneous absolute RadCal.
In this presentation, the GLAMR RadCal data for the Landsat-9 Operational Land Imager (OLI)-2 channels are processed and analyzed. The measured detector ASRs are integrated in the spectral domain to calculate the integrated responsivities to validate the values characterized from the separate absolute RadCal using a broadband light source. The results reveal a spectrally dependent agreement within the combined uncertainty margins of GLAMR and Landsat RadCal. The major sources of uncertainties that lead to these deviations are discussed. These results can demonstrate the capabilities of GLAMR absolute RadCal and can be referenced to estimate the overall uncertainty associated to the GLAMR RadCal of HySICS, which is a key phase of CPF’s independent calibration
Engineered Microalgae Cultivations Systems: Conversion of Wastewater Nutrients Into Biofuels and Bioplastics
Get PDFDissolved Nitrogen and Phosphorus in wastewater can contribute to harmful algae blooms if released into the environment. One technology that can be used to recover dissolved nutrients from wastewater is the Rotating Algae Biofilm Reactor (RABR), which supports microalgae growth in an easily-harvested biofilm and produces nitrogenand phosphorus-rich biomass that can be used to produce slow-release fertilizers, biofuels, and compostable bioplastics. This thesis (1) examines the effects of several environmental factors on the biomass production rate and nutrient removal efficiency of RABRs treating municipal wastewater, (2) quantifies the composition and biofuel yields of microalgae biomass cultivated using a RABR at the Central Valley Water Reclamation Facility (CVWRF) in Salt Lake City, Utah, and (3) evaluates the cost of producing biofuels and bioplastics from the same biofilm.
The effects of four environmental factors (temperature, light intensity, harvesting period, and hydraulic retention time) on biofilm growth and phosphorus removal were evaluated using a statistical design that allows the estimation of changes in the effect of each factor in response to the other factors. This study found that the effect of harvesting period on biofilm growth was influenced by temperature and by light intensity, the effect of light intensity on biofilm growth was influenced by HRT, and the effect of light intensity on phosphorus removal was influenced by temperature. Phosphorus removal could be accounted for primarily by chemical precipitation, with relatively small contributions from direct uptake by the microalgae biofilm. Results from this study were applied to a 11,400-liter pilot RABR operating at CVWRF and used to help determine operating conditions for use in a full-scale model (600,000 gallons of wastewater per day) of the RABR system.
Products like compostable bioplastics, biofuels, and slow-release fertilizers are produced from wastewater-grown microalgae biomass and can be sold to offset wastewater treatment costs. To determine which product should be produced from the algae grown at CVWRF, the biochemical composition and biocrude yields of the CVWRF algae were characterized. Based on this characterization, the technical and economic feasibility of three biomass upgrading processes were selected for evaluation. These processes are (1) the production of bioplastics, (2) the production of bioplastics with a lipid-extraction pretreatment, and (3) the production of biocrude via hydrothermal liquefaction. The production of slow-release fertilizer (dried algae with no further treatment) is also described. Of these processes, the bioplastic production process had the most cost-competitive pricing and the highest carbon and energy efficiency
Target Consumers for Organically Grown Fruit in Utah
Get PDFThis fact sheet provides an overview of target consumers for organically grown fruits and fruit products in Utah. The data examined here comes from an online survey (via Qualtrics) of Utah consumers conducted in 2023. Here, we compare those willing to pay premiums for organically grown fruit and those unwilling to do so, outlining the distinction between them in terms of their demographics, purchasing patterns and shopping habits, as well as their lifestyle and attitudes
Assessing Community Needs and Concerns in Iron County
Get PDFUtah State University Extension conducted a needs assessment to identify priority needs in Iron County. The needs assessment employed a three-phase approach involving interviews, surveys, and data analysis. Results revealed top priority issues, including youth mental health, preparing youth for successful careers, and employment opportunities. The findings will guide Extension programming in addressing community needs effectively
Reducing Food Waste at Home
Get PDFAs food is discarded, resources such as money and water are wasted by producing food that will not be eaten and then transporting it to landfills. There are many solutions for reducing food loss. This fact sheet reviews ways you can build successful habits to address food waste
Recent Climate Change in Utah, 1870-2023
Get PDFClimate change is impacting Utah. Forty-five years of temperature data show that Utah is steadily warming, which, in turn, is driving declines in winter snowpack, shifting the timing and amount of available water, increasing fire risk, and causing ecological change. This fact sheet addresses changes in Utah\u27s temperature, precipitation and snowpack, streamflow, wildfire, and ecology
