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In a recent report, the US National Academy of Science has highlighted the need for sustained, advanced ocean colour research and operations. The report shows that ocean colour satellites provide a unique vantage point for observing the changing biology of our ocean’s surface. Space observations have transformed biological oceanography and are 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. Many coastal applications— such as monitoring for Harmful Algal Blooms (HABs), ecosystem-based fisheries management, and research on benthic habitats including coral reefs and coastal wetlands—require greater spatial resolution than is currently available to resolve the complex optical signals that coastal waters produce. To combat this a team of scientists and engineers in the UK and United States have come together to develop a high resolution ocean colour sensor capable of integration with a custom designed 3U nanosatellite, termed Seahawk.

Sustained ocean color monitoring is vital to understanding the marine ecosystem. It has been identified as an Essential Climate Variable (ECV) and is a vital parameter in understanding long-term climate change. Furthermore, observations can be beneficial in observing oil spills, harmful algal blooms and the health of fisheries. Space-based remote sensing, through MERIS, SeaWiFS and MODIS instruments, have provided a means of observing the vast area covered by the ocean which would otherwise be impossible using ships alone. However, the large pixel size makes measurements of lakes, rivers, estuaries and coastal zones difficult. Furthermore, retirement of a number of widely used and relied upon ocean observation instruments, particularly MERIS and SeaWiFS, leaves a significant gap in ocean color observation opportunities This paper presents an overview of the SeaHawk mission, a collaborative effort between Clyde Space Ltd., the University of North Carolina Wilmington, Cloudland Instruments, and Goddard Spaceflight Center, funded by the Gordon and Betty Moore Foundation. The goal of the project is to enhance the ability to observe ocean color in high temporal and spatial resolution through use of a low-cost, next-generation ocean color sensor flown aboard a CubeSat. The final product will be 530 times smaller (0.0034 vs 1.81m 3 ) and 115 time less massive (3.4 vs 390.0kg) but with a ground resolution 10 times better whilst maintaining a signal/noise ratio 50% that of SeaWiFs. This paper will describe the objectives of the mission, outline the payload specification and the spacecraft platform to support it.

The SeaHawk 3U CubeSat program is funded by the Gordon and Betty Moore Foundation of San Francisco, and managed by John Morrison of the University of North Carolina-Wilmington (UNC-W). Cloudland Instruments is developing HawkEye for SeaHawk. HawkEye is a multispectral ocean color imager of SeaWiFS quality with 120 meter nadir resolution from an orbit altitude of 540 km to provide observation of sub-mesoscale variability for insights into poorly understood mixing dynamics. 120 meter imagery improves ability, relative to SeaWiFS 1km resolution, 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. The optics, filters, and arrays comprise a cube 10 cm on a side to fit a 3U CubeSat manufactured by ClydeSpace of Glasgow Scotland, and provide a 350 km swath cross-track.

The visible and infrared scanner (VIRS), one of three primary sensors on the Tropical Rainfall Measuring Mission (TRMM), has completed its development and test phase at Santa Barbara Remote Sensing and has ben delivered to the Goddard Space Flight Center where it has been integrated on the TRMM spacecraft. VIRS is a five band imaging radiometer with bandpasses similar to those of the Advanced Very High Resolution Radiometers that have flown on the NOAA series of satellites for the last 18 years. VIRS will can a +/- 45 degree swath with a 2.11 kilometer IFOV at nadir from the non-sun-synchronous 350 kilometer TRMM orbit. All five bands will be cooled to 107K at mission start using a passive radiative cooler. The two reflected solar bands will be calibrated on orbit using a solar diffuser. This paper discusses ground calibration and characterization results and proposed post-launch radiometric calibration procedures for the VIRS data.

A new method for performing a preflight calibration of an optical remote sensing instrument with an on-board solar diffuser calibration system is presented. The rationale, method, advantages, disadvantages, error sources, and expected accuracies are discussed. The method was applied to the SeaWiFS sensor to be flown on the SeaStar Satellite.

The solar flux radiometer aboard the Pioneer Venus large probe operated successfully during its descent through the atmosphere of Venus. Upward, downward, and net fluxes from 0.4 to 1.0 micrometers were obtained at more than 390 levels between 185 millibars (at an altitude of approximately 61 kilometers) and the surface. Fluxes from 0.4 to 1.8 micrometers were also obtained between 185 millibars and about the level at which the pressure was 2 atmospheres. Data from 80 to 185 millibars should be available after additional decoding by the Deep Space Network. Upward and downward intensities in a narrower band from 0.59 to 0.66 micrometers were also obtained throughout the descent in order to constrain cloud properties. The measurements indicate three cloud regions above the 1.3-atmosphere level (at an altitude of approximately 49 kilometers) and a clear atmosphere beneath that level. At the 67 degrees solar zenith of the probe entry site, some 15 watts per square meter are absorbed at the surface by a dark ground, which implies that about 2 percent of the solar energy incident on the planet is absorbed at the ground.