SeaHawk-1 CubeSat Ocean Color Mission
The National Research Council recently established the need to sustain and advance satellite ocean color research.1) Space observations have transformed biological oceanography, advancing knowledge of carbon and nitrogen cycling, showing how the ocean's biological processes influence climate, and allowing assessment of changes in primary production (the basis of the marine food chain). Continuous ocean color observation is also essential for monitoring the health of the marine ecosystem and its ability to sustain fisheries. Interrupting the ocean color record would hamper the work of climate scientists, fisheries and coastal resource managers, and other users ranging from the military to oil spill responders. 2) 3)
Earth observing (EO) satellite missions have typically required large spacecraft with multiple payloads, resulting in high costs. For example, the 1997 SeaStar satellite (known later as OrbView-1) with its SeaWiFS (Sea-viewing Wide Field-of-View Sensor) cost more than $100 M, including the sensor, spacecraft, and launch costs. A constellation of EO CubeSats could change this, providing daily or finer temporal resolution and better spatial resolution for dramatically reduced cost.
CubeSats are small, inexpensive satellites built on a concept created by Stanford University's Space Systems Development Laboratory and California Polytechnic State University, intended to provide less-expensive access to space. SeaHawk is a CubeSat fitted with a low-cost, miniature ocean color sensor known as HawkEye that will allow fine-spatial-resolution observations of the ocean. SeaHawk's low cost, mass, and volume, and short development time should enable more similar EO missions in the future. SeaHawk will be 200 times smaller (10 x 10 x 30 cm3 versus 50 x 50 x 200 cm3) and 100 times lighter (~3 kg vs. 309 kg) than OrbView-1, with eight times finer resolution (120 m vs. 1 km) and similar SNR (signal-to-noise ratio).
Two SeaHawk CubeSats are being built over a two-year period (2015–2017) to be launched in 2018, for a cost of $1.7M. SeaHawk-1 has completed its Critical Design Review. There is no technology development involved because commercial subsystems are used throughout. SeaHawk-1 is a 3U CubeSat composed of a 2U standard bus produced by Clyde Space of Glasgow, Scotland, and a 1U HawkEye multispectral ocean color sensor.
HawkEye uses eight spectral bands with ground sample distance of about 120 m from a nominal 540 km polar orbit. HawkEye's specifications are summarized in Table 1. The red rectangle in Figure 1 shows HawkEye's nominal field of view. The system engineering approach driving SeaHawk and HawkEye is based on fitting HawkEye within a 10 cm cube with SeaWiFS radiometry at 120 m nadir resolution from an orbit altitude of 540 km over a 350 km swath. HawkEye's 120 m resolution dramatically improves imaging capabilities compared to the 1 km resolution of OrbView-1's SeaWiFS.
Table 1: HawkEye offers eight SeaWiFS spectral bands with 140 µrad instantaneous field of view per band. SNR: Signal-to-noise ratio. Ltyp: Typical radiance level
* 765 nm SeaWiFS band modified per NASA request
** SeaWiFS Ltyp = 2 HawkEye Ltyp
Figure 1: HawkEye field of view illustrated with a MODIS 4) image of the Santa Barbara channel. The field of view is approximately 350km cross-track from a 540km altitude via pushbroom scan of the 4080 pixel 120m spatial resolution linear arrays. MODIS: Moderate Resolution Imaging Spectroradiometer (image credit: Cloudland Instruments)
Some Background: The University of North Carolina at Wilmington (UNCW) has been funded by the Gordon and Betty Moore Foundation for technology demonstration as “proof of concept” for the development of a “game-changer” in the method to collect and disseminate Ocean Color Data via the use of Nanosatellites. The goal of this project is to enhance the ability of the earth sciences to observe ocean color in high temporal and spatial resolution modes through the use of a low-cost, next-generation, miniature ocean color sensor flown aboard a CubeSat. A CubeSat is a type of nanosatellite with volumes in multiples of 3.0 liter (30cm3), and typically uses commercial off-the-shelf (COTS) components for its electronics. Our team is under contract to develop, construct, launch and operate the SeaHawk CubeSat with a HawkEye Ocean Color Sensor. UNCW will be one of the only non-governmental operators of an Environmental Remote Sensing Satellite — data will be handled by NASA and made available from UNCW to the International Ocean Color Community. 5)
Ocean color satellites provide a unique vantage point for observing the changing biology in the surface ocean. SeaWiFS, which finished its remarkable 13-year mission in 2011, “set-the-bar” transforming biological oceanography and providing data critical to advance our knowledge of how such changes affect important elemental cycles, such as the carbon and nitrogen cycles, and how the ocean’s biological processes influence the climate system and allow us to monitor the biological consequences of that change - to see how the things we do, and how natural variability, affect the Earth's ability to support life and assess changes in primary production, which forms the base of the marine food chain. Using nanotechnology, we constructed an instrument with 8 times the resolution and with a development time and construction cost of both approximately 10% that of SeaWiFS.
Figure 2: Artist's rendition of the SeaHawk-1 satellite on-orbit (image credit: AAC Clyde Space)
Mission Summary 6)
• The goal of the program is to construct and demonstrate the potential scientific applications of two high resolution (~120 m) ocean color instruments to be carried by two 3U (10 cm x 10 cm x 30 cm) CubeSat Platforms:
- ACC Clyde (Glasgow, Scotland) provided the CubeSat bus named SeaHawk
- Cloudland Instruments (California) provided the Hawkeye Sensor
• The Program was funded in 2014 by the Gordon and Betty Moore Foundation
• The program is administered by Dr. John Morrison – UNCW
• NASA provided “advice and review” during the development phase and with formal NASA/HQ Space Act Agreement (2017), will provide services for the collection, processing, calibration, validation, archive and distribution of the data.
• A second Moore Foundation grant was awarded in 2017 to provide the funds for another commercial launch for the second CubeSat and operations of both spacecraft and instruments for a duration of 2 years each.
• In 2021, the University of Georgia Skidaway Institute of Oceanography joint the team, Dr. Sara Rivero-Calle's team will be co-leading the Science Program and Mission Management.
Mission parameters 7)
• Launched: 3 December 2018 8)
• Nominal orbital height = 575 km
• Sun-synchronous around 10:30 a.m.
• 9-day repeat orbit
• Baseline orbital lifetime of 1 year (18-24 month)
• Baseline of 15 scenes per day (200 x 600 km of approximately 120 meter resolution - 100 MB/scene)
• X-band downlink (Wallops & Alaska) data rate of 6 - 100 Mbit/s
- Instrument: less than 1 kg
- Total (spacecraft plus instrument): <5 kg
• Off-the-shelf CCD arrays
• Sensitivity comparable to SeaWiFS
• Open intellectual property and knowledge sharing.
• Power subsystem:
- Clyde Space 3G EPS Motherboard with a Flex daughterboard
- 3G 30 Whr Clyde Space battery
- Solar arrays
• Communication subsystem:
- VHF uplink at 1200 baud/s and UHF downlink at 9.6 kbaud/s
- Syrlinks X-band transmitter (3-50 Mbaud/s / 6-100 Msample/s)
• On-Board computer:
- Clyde Space OBC provides up to 1.8 GB payload data storage
• ADCS (Attitude Determination & Control Subsystem):
- Clyde Space ADCS Motherboard
- Sensors: Course sun sensors, three 2-axis fine sun sensors, magnetometers, rate gyroscopes, GPS
- Actuators: Three-axis reaction wheels, three-axis magnetometers (MTQ)
Figure 3: SeaHawk internal configuration (image credit: NASA)
HawkEye Ocean Color Sensor
The sensor was designed and developed by Cloudland Instruments of Goleta, California with Alan Holmes as PI.
Objectives and benefits: Develop a miniaturized multispectral ocean color imager of SeaWiFS caliber capable of flight on a CubeSat with significantly higher spatial resolution than standard satellite systems, providing observation of sub-mesoscale variability giving insights into mixing dynamics that are poorly understood. High spatial resolution imagery would improve our ability to monitor fjords, estuaries, coral reefs and other near-shore environments where anthropogenic stresses are often most acute and where there are considerable security and commercial interests. Due to low volume, mass and cost, it would become practical to fly constellations of spacecraft, opening up opportunities to significantly improve temporal sampling. The prospect of 10s, if not 10 s of very small Earth Observation spacecraft opens up the possibility of achieving a plethora of science, commercial and military objectives.
Proposed work: Develop, construct, and test a low-cost, multispectral, ocean color sensor with spatial characteristics comparable to SeaWiFS, capable of collection of near-synoptic color data in open-ocean to coastal-margin to near-shore terrestrial environment. The sensor would have the capability of collection of the 8 SeaWiFS bands and be designed with form factor fit into a custom 3U (i.e., 3 Units of 10 cm3) CubeSat; have spatial resolution of 75-150 m and swath of 250-400 km in a 400 - 540 km LEO orbit. It would be built using Commercial Off-The-Shelf (COTS) parts without higher level screening such as typically employed for longer-lived spacecraft instruments.
Figure 4: HawkEye mechanical design concept (image credit: Cloudland Instruments, UNCW) 9)
The HawkEye instrument, flown onboard the SeaHawk CubeSat, was optimized to provide high quality, high resolution imagery (120 meter) of the open ocean, coastal zones, lakes, estuaries and land features. This ability provides a valuable complement to the lower resolution measurements from previous missions like SeaWiFS, MODIS and VIIRS. The SeaHawk CubeSat mission is a partnership between NASA and the University of North Carolina, Wilmington (UNCW), Cloudland Instruments and AAC-Clyde Space and is funded by the Moore Foundation under a grant for the Sustained Ocean Color Observations with Nanosatellites (SOCON). 10)
• June 24, 2021: AAC Clyde Space has received a 135 k USD order to continue operating the SeaHawk-1 satellite from the company’s Operations Center in Glasgow, Scotland, for a further 12 months. 11) 12)
- The satellite, launched in 2018 is part of a partnership between the University of North Carolina Wilmington and NASA, observes the changing biology of the ocean surface and features a compact, multi-spectral camera (HawkEye) developed by Cloudland Instruments. The images captured by the camera are used to analyze the color of the ocean and thus determine the quality of the water.
- The satellite is operated from AAC Clyde Space’s Glasgow Operations Center, with instrument data downloaded to NASA Wallops facility, through the satellite’s X-band downlink. The data is integrated into NASA’s SeaWiFS Data Analysis System (SeaDAS) and is distributed worldwide. Initially, Operations will focus on providing free access to all data that has been collected and processed from mid-April 2021 to the International Ocean Color Community. The satellite is expected to produce around 100 images per week. Data generated enables a greater understanding of the marine food chain, oceanic climate, fisheries and pollution phenomena, enabling to support the health and sustainability of our oceans.
- SeaHawk-1, a 3U CubeSat, is a follow-on mission from the highly successful SeaWiFS (Sea-Viewing Wide field-of-View Sensor) mission, launched in 1997. For more than 20 years, SeaHawk-1 has been able to replicate the performance of the SeaWiFS mission except it is approximately 100 times smaller and lighter and, therefore, more economical, ensuring long term viability of high-quality science missions.
- “It has been quite an experience working with Clyde Space on the design, construction, launch, commissioning, and now operations of SeaHawk-1. As our partners at Clyde Space said when we started on this venture, this satellite is arguably one of the most sophisticated 3U CubeSats ever conceived. We have just commissioned a satellite the size of a shoebox that’s travelling at 7.5 km/s, at an altitude of about 600km with a better downlink rate than the broadband into my house providing scientific quality data on ocean ecology,” said John M. Morrison, UNCW Principal Investigator.
- “AAC Clyde Space are delighted to continue to support the SeaHawk-1 mission. Academia, government agencies and industry are joining forces like never before to improve environmental surveillance and generate reliable data, filling in the gaps of our understanding for informed decision making. SeaHawk-1 is a prime example of this, Sustained Ocean Color Monitoring is vital to understanding the marine ecosystem and in turn climate change,” said AAC Clyde Space CEO, Luis Gomes.
• As of June 21st 2021, SeaHawk-1 Cubesat outfitted with the HawkEye Ocean Color Imager has completed on-orbit “Commissioning” and is entering into a period of phased startup of “Operations"! (Ref. 5).
- Hawkeye imagery will be made available free of charge via the NASA Ocean Biology Distributed Active Archive Center (OB.DAAC) on NASA’s Ocean Color Website https://oceancolor.gsfc.nasa.gov. In addition, NASA’s free software package for the processing, display and analysis of ocean color data known as SeaDAS (https://seadas.gsfc.nasa.gov/) has been updated to include support for HawkEye.
• March 22, 2019: The University of North Carolina Wilmington (UNCW) together with NASA, AAC Clyde Space, Cloudland Instruments, and the Gordon and Betty Moore Foundation, is pleased to announce the successful acquisition and retrieval of SeaHawk-1 CubeSat’s first ocean color image from space. On March 22nd, it was downlinked via X-band from the SeaHawk-1 CubeSat to the ground station at NASA Wallops and immediately transferred to NASA Goddard, where it was processed. 13)
Figure 5: This first SeaHawk-1 engineering test image was captured by the HawkEye instrument on March 21st, 2019 at 18:47 UT from an altitude of 588 km and superimposed on Google Map data © 2019 Google, INEGI. At the current altitude that SeaHawk is flying, the pixel resolution of the HawkEye instrument is approximately 130 meters (425 feet) giving us an image size of approximately 6000 lines along track (780 km or 485 mi) x 1800 pixels across track (234 km or 145 mi), image credit: UNCW, AAC Clcde Space, NASA)
Figure 6: The true color full resolution closeup of the region from south of Monterey Bay to north of San Francisco was produced by combining three of the Hawkeye bands (red band-6 (670 nm), green band-5 (555 nm) and blue band-2 (443 nm), image credit: UNCW, AAC Clyde Space, NASA)
Figure 7: Another view of Monterey Bay in which a slightly different combination of three bands (red band 6 (670 nm), green band 5 (555 nm) and blue band 3 (490 nm) were used to bring out some of the features that can be seen in the water (image credit: UNCW)
Figure 8: Crorophyll-a concentration (image credit: UNCW, AAC Clyde Space, NASA)
Mission and Spacecraft
SeaHawk-1 is a 3U CubeSat (size 30 x 10 x 10 cm with a mass of ~5 kg) designed and built by AAC Clyde Space and launched on 3 December 2018 aboard SpaceX Falcon 9. The SeaHawk-1 CubeSat was one of the 64 satellites included in the Spaceflight SSO-A Small Sat Express: their first dedicated ride-share mission for small satellites. SeaHawk-1 is also the first 3U CubeSat specifically designed to carry an ocean color instrument payload (HawkEye). The goal of this proof-of-concept mission is to provide free high-spatial resolution images of Earth’s coastal regions. HawkEye, designed by Cloudland Instruments, is an 8-band multispectral instrument similar to SeaWiFS (one of the most successful ocean color missions to date). It differs in that: it was miniaturized (10 x 10 x 10 cm) to fit inside the CubeSat, band 7 was modified to improve atmospheric correction, all bands were designed not to saturate over land, and the entire sensor was built with low-cost, off-the-shelf materials. But one of the biggest contributions of SeaHawk-1 is its 130-meter spatial resolution. This high resolution (~8 times better than SeaWiFS or standard global ocean color satellites) ocean color imagery will resolve sub-mesoscale features and will advance our understanding of key coastal processes and ecosystems. Some examples of potential areas of application include early detection of harmful algal blooms, glacier dynamics, threatened coral reefs, storm water runoffs, etc., all of which have direct impact in human well-being or livelihood. SeaHawk-1 follows a sun-synchronous orbit an altitude of ~590 km, orbiting 15-times a day with a current repeat time of about 18-days. SeaHawk-1 is one of two identical CubeSats, and SeaHawk-2 is expected to be launched within the next year, potentially reducing the time needed to re-image any given location. Once SeaHawk-1 is fully commissioned and begins operations, data will be available at no cost through NASA’s Ocean Biology Processing Group (https://oceancolor.gsfc.nasa.gov) and UNCW (https://uncw.edu/socon/mission.html). In the near future, the scientific community will also be able to submit requests for image acquisition (e.g. for field support) through UNCW (https://uncw.edu/socon/requests.html ). This project is funded by the Gordon and Betty Moore Foundation through Grant GBMF4526 to UNCW at Wilmington, Department of Physics and Physical Oceanography and Space Act Agreement 450-AGMT-0149 between NASA and UNCW.
UNCW's Satellite Oceanography Lab
Faculty members from the Department of Physical Oceanography and the students from UNCW's Student CubeSat Lab participated in the joint telecon on Friday, when the first image was downlinked to the ground station at NASA Wallops. The UNCW CubeSat Lab is a newly formed student association that was born in 2018 as a result of the genuine interest in the project by some students from UNCW's Master's Degree in Data Science. The students are now involved in several projects under the guidance of advisors from the Department of Physical Oceanography and the Data Science Program. Students in the UNCW CubeSat Club presented a poster at the First NC Space Grant Student Symposium in April 2019.
Figure 9: Faculty members Prof. Till Wagner, Prof. Frederick Bingham and Dr. Sara Rivero Calle celebrating the succesful retrieval of SeaHawk-1's first light image with the students from UNCW's CubeSat Lab (image credit: UNCW)
The target location for the first light image was discussed with the entire SeaHawk team. The decision was based on certain requisites that included: a latitudinal range between 20-40 degrees, low probability of cloud cover or sun glint, a combination of land and ocean, and the CubeSat path. NASA Goddard, MD then scheduled the image acquisition and was in charge of processing the raw data up to level 1-A with the assistance of Cloudland Instruments and AAC Clyde Space.
Figure 10: Left: Gene Carl Feldman, Liang Hong and Alicia Scott scheduling the first image acquisition at NASA Goddard. Right: Image processing group at NASA Goddard analyzing the first HawkEye image within minutes of the downlink (image credit: NASA)
Meanwhile NASA’s Near-Earth Network (NEN) ground station in Wallops, VA was in charge of downlinking the image from the CubeSat via X-Band and sending it to NASA Goddard for processing.
Figure 11: On the left you can see the location of SeaHawk-1 during the overpass and on the right, a picture of the signal received at NASA Wallops. On the bottom right there is a picture of a similar test done during the first overpass of the SeaWiFS mission 22 years earlier! (image credit: NASA)
1) C. F. Schueler, James A. Yoder, David Antoine, C. E. del Castillo, Robert H. Evans, C. Mengelt, Curtis Mobley, JimenaSarmiento, S. Sathyendranath, D. A. Siegel, Cara Wilson, ”Assessing the Requirements for Sustained Ocean Color Research and Operations,” National Academies Press, Washington DC, 2011, The National Academies Press, https://doi.org/10.17226/13127
2) Carl Schueler, Alan Holmes, ”Monitoring coastal ocean color with low-cost CubeSats,” SPIE, 13 September 2011, URL: https://spie.org/news/
3) Carl Schueler, Alan Holmes, ”SeaHawk CubeSat system engineering,” Proceedings of SPIE, Vol. 9977, 'Remote Sensing System Engineering VI; 99770A, 19 September 2016,' https://doi.org/10.1117/12.2242298, Event: SPIE Optical Engineering + Applications, 2016, San Diego, California, United States
7) ”SeaHawk Mission Summary,” NASA/GSFC, URL: https://oceancolor.gsfc.nasa.gov/data/hawkeye/summary/
”ÅAC Microtec confirms successful launch of SeaHawk-1,
ground-breaking ocean health monitoring CubeSat,” AAC Clyde Space
Press Releases, 04 December 2018, URL: https://investor.aac-clyde.space
11) ”AAC Clyde Space Receives SeaHawk-1 Smallsat Ops Renewal Contract,” Satnews, 24 June 2021, URL: https://news.satnews.com/2021/06/24/
12) ”Big Things Come in Very Small Packages: A New Way of Looking at the Ocean,” UNCW, 24 June 2021, URL: https://uncw.edu/news/2021/06/
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).