Alan W. Holmes

Preflight solar-based calibration of SeaWiFS

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.

Low dark current InGaAs detector arrays for night vision and astronomy

Aerius Photonics has developed large InGaAs arrays (1K x 1K and greater) with low dark currents for use in night vision applications in the SWIR regime. Aerius will present results of experiments to reduce the dark current density of their InGaAs detector arrays. By varying device designs and passivations, Aerius has achieved a dark current density below 1.0 nA/cm2 at 280K on small-pixel, detector arrays. Data is shown for both test structures and focal plane arrays. In addition, data from cryogenically cooled InGaAs arrays will be shown for astronomy applications.

Overview of the SeaWiFS ocean sensor

SeaWiFS, the sea-viewing wide field-of-view sensor, will bring to the ocean community a welcomed and improved renewal of the ocean color remote sensing capability that was lost when the Nimbus-7 coastal zone color scanner (CZCS) ceased operating in 1986. Because of the role of phytoplankton in the global carbon cycle, data obtained from SeaWiFS will be used to assess the oceans role in the global carbon cycle, as well as in other biogeochemical cycles. SeaWiFS data will be used to help determine the magnitude and variability of the annual cycle of primary production by marine phytoplankton and to determine the distribution and timing of spring blooms. The observations will help to visualize the dynamics of ocean and coastal currents, the physics of mixing, and the relationship between ocean physics and large-scale patterns of productivity. The data from SeaWiFS will help fill the gap in ocean biological observations between those of CZCS and those of the moderate resolution imaging spectrometer (MODIS) on the Earth Observing Satellite-A (EOS-A).

SeaWiFS transfer-to-orbit experiment

We present the results of an experiment designed to measure the changes in the radiometric calibration of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) from the time of its manufacture to the time of the start of on-orbit operations. The experiment uses measurements of the Sun at the manufacturers facility to predict the instrument outputs during solar measurements immediately after launch. Because an onboard diffuser plate is required for these measurements, the experiment measures changes in the instrument-diffuser system. There is no mechanism in this experiment to separate changes in the diffuser from changes in the instrument. For the eight SeaWiFS bands, the initial instrument outputs on orbit averaged 0.8% higher than predicted with a standard deviation of 0.9%. The greatest difference was 2.1% (actual output higher than predicted) for band 3. The estimated uncertainty for the experiment is 3%. Thus the transfer-to-orbit experiment shows no changes in the radiometric sensitivities of the SeaWiFS bands--at the 3% level--from the completion of the instruments manufacture to its insertion into orbit.

Characterization and calibration results from the Visible and Infrared Scanner (VIRS) for the Tropical Rainfall Measuring Mission (TRMM)

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.

SEAHAWK: A nanosatellite mission for sustained ocean observation

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.

Hawkeye radiometric calibration methodology.

Hawkeye is an ocean color instrument designed, manufactured and characterized at Cloudland Instruments, CA. It is a push broom instrument that has 8 spectral bands similar to SeaWiFS and a spatial resolution of 120 m. Each spectral band has 1800 detectors (pixels) and all 14,000 detectors (pixels) need to be calibrated independently. This paper describes the preliminary design of on-orbit calibration method to correct for the instrument response’s temperature sensitivity, scan angle dependency in radiometric sensitivity, relative spectral response (RSR), nonlinearity, and polarization sensitivity. We will provide a brief description on how each of the calibration parameters are used to address the instrument characteristics and how the calibration parameters are derived from instrument test data and use to retrieve ocean color products.

SeaHawk: an advanced CubeSat mission for sustained ocean colour monitoring

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 1.81m3) 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.

SeaHawk CubeSat system engineering

The SeaHawk 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 SeaHawk’s multispectral ocean color imager, known as HawkEye. HawkEye optics, filters, detector arrays, and electronics form a cube just 10 cm on a side to fit the SeaHawk 3U CubeSat manufactured by Clyde Space, Glasgow Scotland. This paper discusses the system engineering approach to design, develop, complete, test, integrate and launch two SeaHawk CubeSats in three years within a

HawkEye: CubeSat SeaWiFS update

1.7M budget.