Results for “Ocean Color Instrument”

NASA NTRS2018

Hawkeye Ocean Color Instrument – Performance Summary

Hawkeye is an ocean color instrument that is part of the SeaHawk satellite developed for SOCON, the Sustained Ocean Color Observations using Nanosatellites program funded by the Gordon and Betty Moore Foundation and managed by the University of North Carolina – Wilmington (UNC-W). HawkEye has spectral characteristics similar to SeaWiFS, but with 8 times finer resolution and a smaller field of view more appropriate for lakes, rivers, and near-shore terrestrial environments. With a volume of only 10 X 10 X 10 cm (a CubeSat 1U), it can produce 8 bands of image data in a single pass, each with 1800 x 6000 pixels, with a resolution of 120 meters per pixel. This paper will present a short summary of instrument design, the spacecraft interface, and “lessons learned” during this effort. Scientists considering using linear arrays in a pushbroom mode for remote sensing will find this useful. Much of the discussion will center on optical performance, such as flat field calibration, polarization effects, stray light, out-of-band response, and exposure linearity. Images from field tests will be shown.The Hawkeye instrument is an ocean color measuring instrument designed to fly on the SeaHawk satellite developed for SOCON, the Sustained Ocean Color Observations using Nanosatellites program funded by the Gordon and Betty Moore Foundation and managed by the University of North Carolina – Wilmington (UNC-W). The Hawkeye instrument measures ocean color in 8 spectral bands, similar to SeaWiFS, except Band 7, which is shifted to a slightly lower wavelength to avoid the oxygen absorption feature that a wider band overlapped on SeaWiFS. The instrument is approximately 1/3rd the volume of the entire satellite, which is a 3U Cubesat manufactured by Clydespace in Glasgow, Scotland. The purpose of this instrument is to ascertain the quality of ocean color data possible with such a small, inexpensive instrument and bus. The nominal orbit is 540 km, and the nominal pixel geometric instantaneous field of view (GIFOV) 120 meters on a side. Each band will produce an image 1800 x 6000 pixels in size, for a total field of view of 216 X 720 km.2) DESIGN CONCEPTThe Hawkeye instrument uses linear arrays in pushbroom mode to collect data over a two dimensional area. The instrument has 4 linear CCD arrays, the Onsemi KLI-4104, to collect the 8 bands of data. Figure 1 illustrates the optical design for two bands, sharing a single array.

Hawkeye↗

NASA NTRS2023

Lessons Learned From Evaluation and Mitigation of Space Charging Threat Due to Use of Isolated (Hybrid) Bearings on the Pace Ocean Color Instrument

A high precision, high resolution Ocean Color Instrument (OCI) was developed for the Plankton, Aerosol, Cloud ocean Ecosystem (PACE) mission which required the use of electrically isolated Hybrid Bearings (silicon nitride balls). While desirable for technical performance of the instrument, this application caused portions of the instrument to become electrically isolated and come under threat of space charging effects from charged particles and the resultant differential charging. An evaluation of the environment, susceptibility of the components, such as bearings and electronics, and mitigation strategies were performed. As part of that process, simulations of the charging environment, analysis of internal mechanism charging and prediction of most likely discharge paths, testing of the bearings for susceptibility as well as resulting damage were performed and analyzed. Additionally, a novel method to deal with charging was developed. Considerations for dealing with electrically isolated mechanisms, results of the above-mentioned efforts as well as lessons learned are presented.

space charging↗

NASA NTRS2019

Retrieving Aerosol Characteristics From the PACE Mission, Part 1: Ocean Color Instrument

NASA’s Plankton, Aerosol, Clouds, ocean Ecosystem (PACE) satellite mission is scheduled to launch in 2022, with the Ocean Color Instrument (OCI) on board. For the first time reflected sunlight from the Earth across a broad spectrum from the ultraviolet (UV: 350 nm) to the short wave infrared (SWIR: 2260 nm) will be measured from a single instrument at 1 km spatial resolution. While seven discrete bands will represent the SWIR, the spectrum from 350 to 890 nm will be continuously covered with a spectral resolution of 5 nm. OCI will thus combine in a single instrument (and at an enhanced spatial resolution for the UV) the heritage capabilities of the Moderate resolution Imaging Spectroradiometer (MODIS) and the Ozone Monitoring Instrument (OMI), while covering the oxygen A-band (O2A). Designed for ocean color and ocean biology retrievals, OCI also enables continuation of heritage satellite aerosol products and the development of new aerosol characterization from space. In particular the combination of MODIS and OMI characteristics allows deriving aerosol height, absorption and optical depth along with a measure of particle size distribution. This is achieved by using the traditional MODIS visible-to-SWIR wavelengths to constrain spectral aerosol optical depth and particle size. Extrapolating this information to the UV channels allows retrieval of aerosol absorption and layer height. A more direct method to derive aerosol layer height makes use of O2A absorption methods, despite the relative coarseness of the nominal 5 nm spectral resolution of OCI. Altogether the PACE mission with OCI will be an unprecedented opportunity for aerosol characterization that will continue climate data records from the past decades and propel aerosol science forward toward new opportunities.

PACE↗

NASA NTRSDate not supplied

Pulse Response of the Short-Wave Infrared Detection System of the Ocean Color Instrument for the NASA Pace Mission

The Ocean Color Instrument (OCI) on NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission is a hyperspectral Earth imager with a spatial resolution of 1 km x 1 km and a spectral resolution of 5 nm in 2.5 nm steps over 342-887 nm. In addition, OCI provides 7 discrete bands in the 940-2260 nm Short-Wave InfraRed (SWIR) range. The front-end optical imager is a rotating mirror-based system that images the ground scene onto a slit with an instantaneous field of view of 16 km x 1 km. For the SWIR bands, the slit-image is re-imaged onto a 16x1 micro-lens array that effectively acts as the focal plane since each lens element is fiber coupled to wavelength filtered InGaAs and HgCdTe Photo Diodes (PDs). The pulse response of the detection system is critical to OCI SWIR performance. We find that PDs introduce an inherent slow tail in the pulse response due to slow diffusion moving carriers in their n and p regions. We show that this introduces response errors ranging from 1 down to 0.01 % for up to tens of science pixels after the pulse depending on the PD design and materials. It is shown that the response is distinctly different for the InGaAs and HgCdTe PDs. We explain how the front-end design can further increase this error. Finally, we detail the cause of the slow pulse response tail, how to model it, its impact on OCI performance and how it is characterized and corrected to meet OCI requirements.

ocean color↗

NASA NTRS2023

Pulse Response of the Short-Wave Infrared Detection System of the Ocean Color Instrument for the NASA PACE Mission

The Ocean Color Instrument (OCI) on NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission is a hyperspectral Earth imager with a spatial resolution of 1 km x 1 km and a spectral resolution of 5 nm in 2.5 nm steps over 342-887 nm. In addition, OCI provides 7 discrete bands in the 940-2260 nm Short-Wave InfraRed (SWIR) range. The front-end optical imager is a rotating mirror-based system that images the ground scene onto a slit with an instantaneous field of view of 16 km x 1 km. For the SWIR bands, the slit-image is re-imaged onto a 16x1 micro-lens array that effectively acts as the focal plane since each lens element is fiber coupled to wavelength filtered InGaAs and HgCdTe Photo Diodes (PDs). The pulse response of the detection system is critical to OCI SWIR performance. We find that PDs introduce an inherent slow tail in the pulse response due to slow diffusion moving carriers in their n and p regions. We show that this introduces response errors ranging from 1 down to 0.01 % for up to tens of science pixels after the pulse depending on the PD design and materials. It is shown that the response is distinctly different for the InGaAs and HgCdTe PDs. We explain how the front-end design can further increase this error. Finally, we detail the cause of the slow pulse response tail, how to model it, its impact on OCI performance and how it is characterized and corrected to meet OCI requirements.

ocean color↗

NASA NTRSDate not supplied

Optical and Detector Design of the Ocean Color Instrument for the NASA Pace Mission

The Ocean Color Instrument (OCI) on NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem mission is a hyperspectral imager with high SNR, precision and dynamic range, and with a very low striping artifact level in the 342-887 nm wavelength range with a spectral resolution of 5 nm in 2.5 nm steps, providing a significant technological advancement over previous ocean imagers. To achieve this, OCI is designed with specialized optical imaging and opto-electronic detection systems that push the boundaries of several state-of-the-art technologies. This paper provides an overview of these systems together with their achieved performances and discussions of their key design challenges.

Remote sensing↗

NASA NTRSDate not supplied

Optical and Detector Design of the Ocean Color Instrument for the NASA Pace Mission

The Ocean Color Instrument (OCI) on NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem mission is a hyperspectral imager with high SNR, precision and dynamic range, and with a very low striping artifact level in the 342-887 nm wavelength range with a spectral resolution of 5 nm in 2.5 nm steps, providing a significant technological advancement over previous ocean imagers. To achieve this, OCI is designed with specialized optical imaging and opto-electronic detection systems that push the boundaries of several state-of-the-art technologies. This paper provides an overview of these systems together with their achieved performances and discussions of their key design challenges.

Remote sensing↗

NASA NTRSDate not supplied

Spectral Measurement Errors due to CCD Serial Pixel-to-Pixel Readout Interference in the Ocean Color Instrument of the NASA PACE Mission

The Ocean Color Instrument on NASA’s PACE mission is a hyperspectral imager with a spatial resolution of 1km x 1km and spectral resolution of 5nm in 2.5nm steps over 320-890nm. The detection system is based on two Charge-Coupled Devices (CCDs) operating in Time Delay Integration (TDI) mode to achieve high signal-to-noise ratio. The front-end optical imager is a rotating mirror-based system that images the ground-scene onto a slit with a field of view of 16km x 1km. The slit-image is re-imaged and wavelength dispersed on the CCDs. As the ground-scene moves through the slit, it moves along the CCD columns as charge is moved along with it. The accumulated charge at the end of each column is collected in a serial pixel. Each of the 16 CCD outputs read out 32 columns of the same ground scene spaced 0.625nm apart. The 32-pixel serial register is swiftly read out before the next TDI cycle. The telescope is spinning at 5.77Hz to achieve the required spatial resolution. This results in a serial pixel readout speed of 8.5MHz. Each serial read-cycle goes through a reset and video period that are each sampled to create a low-noise correlated double sample value. This only allows 59ns for the reset and video to be asserted and settled before sampling. Due to the short time period, the response of the CCD exhibits serial pixel-to-pixel readout interference as the reset and video signals do not have time to fully settle before sampling. Each serial pixel value therefore has a dependence on the value of the preceding pixel value. This leads to a spectral measurement error of up to 0.3%. We explain the operation of the detection system, the behavior of the interference and the resulting wavelength error with results from ground testing and on-orbit characterization.

Ulrik B Gliese↗

NASA NTRSDate not supplied

Spectrally Dependent Radiometric Measurement Errors Due to Ccd Serial Pixel-to-Pixel Readout Interference in the Ocean Color Instrument of the NASA PACE Mission

The Ocean Color Instrument on NASA’s PACE mission is a 322 887 nm hyperspectral imager with 1 km x 1 km nadir spatial resolution and 5 nm spectral resolution utilizing charge-coupled devices (CCDs) operating in Time Delay Integration (TDI) mode where each TDI column represents a different wavelength in 0.625 nm increments. After TDI, the charge is moved into serial output pixels and read out. The spatial resolution requires an 8.5 MHz readout rate. This only allows 59 ns for the CCD reset and video to be asserted and settled before sampling. The response exhibits serial pixel-to-pixel readout interference due to the lack of full settling. Each serial pixel value has a dependence on the value of the preceding pixel value. This leads to a spectrally dependent radiometric measurement error of up to 0.3 %. We explain the operation of the detection system, the behavior of the interference, and show the resulting measurement error based on data from both ground testing and on-orbit characterization.

Remote Sensing↗

NASA NTRS2024

Spectrally Dependent Radiometric Measurement Errors Due to CCD Serial Pixel-to-Pixel Readout Interference in the Ocean Color Instrument of the NASA PACE Mission

The Ocean Color Instrument on NASA’s PACE mission is a 322 887 nm hyperspectral imager with 1 km x 1 km nadir spatial resolution and 5 nm spectral resolution utilizing charge-coupled devices (CCDs) operating in Time Delay Integration (TDI) mode where each TDI column represents a different wavelength in 0.625 nm increments. After TDI, the charge is moved into serial output pixels and read out. The spatial resolution requires an 8.5 MHz readout rate. This only allows 59 ns for the CCD reset and video to be asserted and settled before sampling. The response exhibits serial pixel-to-pixel readout interference due to the lack of full settling. Each serial pixel value has a dependence on the value of the preceding pixel value. This leads to a spectrally dependent radiometric measurement error of up to 0.3 %. We explain the operation of the detection system, the behavior of the interference, and show the resulting measurement error based on data from both ground testing and on-orbit characterization.

Remote Sensing↗

NASA NTRS2022

Infrared Spectral Responses of the Ocean Color Instrument (OCI) Pre-assembly and Integration

The Ocean Color Instrument (OCI) to go on the Plankton, Aerosol, Cloud, ocean Ecology (PACE) Earth-observing satellite has a Short-wave infrared (SWIR) Detection Assembly (SDA). This SDA is used to measure upwelling radiation in seven discrete bands from 940 to 2260 nm. There are redundant measurements of each band for a total of 32 physical channels, which includes optical components through to detection. The relative spectral response (RSR) is measured for each channel, which is needed when accounting for the spectral distribution of sensed radiance. From the RSR, single-value performance metrics are computed including the center wavelength, the full width at half of the maximum (FWHM), and the full width at 1% of the maximum (FW1P). Besides in-band responses, the out-of-band rejection ratio (OOBRR) is also calculated for each of the channels, which is a measure of the sensitivity outside the band of interest. We find that all 32 SDA detection channels meet the spectral response requirements at the qualification temperatures at which tests were conducted.

PACE↗

NASA NTRS2018

Imaging Technique for High Precision Measurement of Detector Stability for the Ocean Color Instrument

One of the new projects by NASA to explore environmental change is the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) spacecraft. The primary instrument aboard the PACE spacecraft is the Ocean Color Instrument (OCI), an advanced optical spectrometer that will measure the color of the ocean from the ultraviolet to shortwave infrared range for the purpose of observing and monitoring ocean and coastal biology. As part of the optical alignment testing that must be completed before the instrument is built, the measurement stability of the detectors at space flight operating temperatures must be determined to ensure alignment is maintained. Therefore, this project focuses on the development of an imaging technique that adheres to testing requirements and can be used to determine the stability of the OCI detector. The movements of targets affixed to a high-precision stage were analyzed through an image processing program to test the ability of the imaging technique to detect very small (under 10 micrometers) movements. It was found that movements as small as half a pixel (~6 microns) and 1 pixel (~12 microns) were able to be accurately and consistently detected with this imaging technique. This project found that the designed image analysis technique fulfills testing and measurement requirements and will be an effective metrology technique for the OCI detector stability test.

Optics↗

NASA NTRSDate not supplied

Initial On-Orbit Spectral Calibration of the PACE Ocean Color Instrument

The NASA Plankton, Aerosol, Cloud, and ocean Ecosystem (PACE) mission Project Science Team has used Ocean Color Instrument (OCI) measurements of Fraunhofer lines in spectra of sunlight reflected by the solar diffuser and measurements of atmospheric absorption bands in cloudtop and ocean spectra to characterize the spectral calibration of OCI on orbit. Multiple lines have been analyzed for both the ultraviolet to visible (UVVIS, 340−607 nm) and visible to near-infrared (VISNIR, 597−897 nm) grating spectrographs. The spectrographs yield hyperspectral observations with 5 nm bandwidths and 0.625 nm sampling intervals. The on-orbit observations have been compared with the prelaunch spectral calibration of OCI performed by the Goddard Laser for Absolute Measurement of Radiance (GLAMR) during thermal vacuum testing to track any changes in the calibration since launch. The calibration analyzed the line positions and strengths for the Fraunhofer lines for each spectrograph by comparing the solar spectra measured by OCI with predicted solar spectra derived from the solar reference spectrum and the BRDF of the solar diffuser, convolved with the OCI relative spectral responses. The calibration also compared the line positions of the atmospheric absorption bands with the model transmissions used by the PACE Project. The line position comparisons show that the root mean square (RMS) spectral difference between the measured and predicted spectra is 0.15 nm, the average spectral shift is 0.062 nm, and the residual spectral dispersion over the wavelength range of the Fraunhofer lines is 0.17 nm. All three estimates of the spectral accuracy of OCI meet the instrument functional requirement of a spectral accuracy of 0.5 nm and are well within the 0.625 nm sampling interval of the data. The line strength comparisons between measured and predicted spectra are essentially the same. These results show that the spectral calibration of OCI on orbit has not drifted since the prelaunch calibration of OCI by GLAMR and that the on-orbit spectral calibration of OCI is stable over time. These results also provide a baseline for monitoring the future spectral performance of OCI on orbit.

Radiometric Calibration↗

NASA NTRS2016

Aerosol Absorption Retrievals from the PACE Broad Spectrum Ocean Color Instrument (OCI)

The PACE (Pre-Aerosol, Clouds and ocean Ecosystem) mission, anticipated for launch in the early 2020s, is designed to characterize oceanic and atmospheric properties. The primary instrument on-‐board will be a moderate resolution (approximately 1 km nadir) radiometer, called the Ocean Color Instrument (OCI). OCI will provide high spectral resolution (5 nm) from the UV to NIR (350 - 800 nm), with additional spectral bands in the NIR and SWIR. The OCI itself is an excellent instrument for atmospheric objectives, providing measurements across a broad spectral range that in essence combines the capabilities of MODIS and OMI, but with the UV channels from OMI to be available at moderate resolution. (Image credit: PACE Science Definition Team Report). Objective: Can we make use of the UV-SWIR measurements to derive information about aerosol absorption when aerosol loading is high?

aerosols↗

NASA NTRSDate not supplied

NASA’s PACE Ocean Color Instrument Thermal Design Evolution: from Goddard’s Instrument Design Lab through Flight Development

NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, set to launch in 2024, seeks to provide data continuity for the ocean color, aerosol and cloud measurements acquired by NASA’s on-orbit Earth Science observatories since the 1990s. It will accomplish this through its Ocean Color Instrument (OCI), an optical spectrometer being developed for hyper-spectral measurements in the ultraviolet-to-near-infrared band between 340 nm and 2260 nm. Although OCI’s instrument architecture will provide greater insight and resolution than its predecessors in this wavelength range, the engineering required to achieve this also poses a greater challenge. In thermal engineering, this translates to a more complex thermal control approach to address high heat dissipations, stringent stabilities, the volume of heat that requires transport, and changing thermal environments due to tilting of the entire instrument ±20° twice per orbit. This current work explores how the PACE OCI instrument design has evolved from its initial conception in NASA Goddard’s Instrument Design Laboratory (IDL) to the current iteration of its flight design. The IDL studies explored three separate instrument configurations and two spatial resolutions per configuration, which were then down selected to a single instrument type and spatial resolution for flight instrument development. OCI subsequently went through major project milestones, including Preliminary Design Review (PDR), Critical Design Review (CDR), Pre-Environmental Review (PER) and Pre-Ship Review (PSR), with significant design updates along the way. This paper aims to provide a comprehensive account of OCI’s thermal control architecture evolution and the engineering drivers that have shaped it, with the goal of identifying trends spanning the full instrument development timeline to inform and advance future instrument thermal designs.

PACE↗

NASA NTRSDate not supplied

NASA’s PACE Ocean Color Instrument Thermal Design Evolution: from Goddard’s Instrument Design Lab through Flight Development

NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, set to launch in 2024, seeks to provide data continuity for the ocean color, aerosol and cloud measurements acquired by NASA’s on-orbit Earth Science observatories since the 1990s. It will accomplish this through its Ocean Color Instrument (OCI), an optical spectrometer being developed for hyper-spectral measurements in the ultraviolet-to-near-infrared band between 340 nm and 2260 nm. Although OCI’s instrument architecture will provide greater insight and resolution than its predecessors in this wavelength range, the engineering required to achieve this also poses a greater challenge. In thermal engineering, this translates to a more complex thermal control approach to address high heat dissipations, stringent stabilities, the volume of heat that requires transport, and changing thermal environments due to tilting of the entire instrument ±20° twice per orbit. This current work explores how the PACE OCI instrument design has evolved from its initial conception in NASA Goddard’s Instrument Design Laboratory (IDL) to the current iteration of its flight design. The IDL studies explored three separate instrument configurations and two spatial resolutions per configuration, which were then down selected to a single instrument type and spatial resolution for flight instrument development. OCI subsequently went through major project milestones, including Preliminary Design Review (PDR), Critical Design Review (CDR), Pre-Environmental Review (PER) and Pre-Ship Review (PSR), with significant design updates along the way. This paper aims to provide a comprehensive account of OCI’s thermal control architecture evolution and the engineering drivers that have shaped it, with the goal of identifying trends spanning the full instrument development timeline to inform and advance future instrument thermal designs.

PACE↗

NASA NTRS2019

Calibration Plan for the Ocean Color Instrument (OCI) Engineering Test Unit

The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission will launch no earlier than summer 2022. The primary payload is the Ocean Color Instrument (OCI). OCI is a hyperspectral imaging radiometer that will measure top-of-atmosphere radiances from 340nm to 2260nm at approximately 1km spatial resolution. The spectral resolution will be 5nm from 340nm to 890nm to enable the production of innovative ocean color products on a global scale (OCI will provide global coverage every 2 days). There are 7 different multispectral bands in the shortwave infrared to support atmospheric correction for ocean color and aerosol and cloud studies. Ocean color applications require state of the art radiometric accuracy (approximately 0.5%, excluding the absolute calibration uncertainty). Considerable effort has been invested in the planning of the prelaunch calibration campaign and the on-orbit calibration capabilities. This paper describes the current plans for the prelaunch calibration and characterization campaign of the OCI Engineering Test Unit (ETU), which is scheduled to begin towards the end of 2019, and expected to conclude April 2020. The prelaunch calibration campaign will characterize all sensor characteristics that are expected to influence radiometric sensitivity: absolute calibration (i.e. radiometric gains), signal to noise ratio, nonlinearity, response versus scan angle, dynamic range, straylight, crosstalk, and sensitivities to polarization and temperature. In addition to these characterization tests (which will only be performed once for the ETU), two types of tests have been developed that monitor the evolution of several OCI radiometric characteristics: a Limited Performance Test (LPT, expected duration about 8 hours), and a Comprehensive Performance Test (CPT, expected duration about 2 days).

Meister, Gerhard↗

NASA NTRS2022

Infrared Spectral Responses of the Ocean Color Instrument (OCI) Pre-assembly and Integration

Spectral characterizations were made of the Ocean Color Instrument (OCI) short-wave infrared (SWIR) Detection Subassembly (SDS) responses (940–2260 nm) prior to their integration. Using modulated output light from a Fourier transform spectrometer, the in-band relative spectral responses of the nine different configurations of SDSs were found along with out-of-band (OOB) sensitivity. From these spectral responses, the center wavelengths (λ0), full widths at half of the maximum, full widths at 1% of the maximum, and OOB rejection ratios were determined. All spectral parameters are within requirements. There are 2–8 repeats of each configuration, and the 1 σ spread among repeats is largest for the 1250 nm and 1615 nm high-gain configurations and is greater than 1 nm. The engineering requirement is for these values to be within ±4 nm and ±10 nm, respectively, of 19 the nominal λ0. There is also a λ0 temperature dependence, which is expected. This temperature dependence is nearly a linear function of wavelength with a 9.5 × 10−3 nm K−1 relationship on average.

PACE↗