NASA's Coastal and Ocean Airborne Science Testbed (COAST): Early Results
L. Guild1, J. Dungan1, M. Edwards1, P. Russell1, J. Morrow2, S. Hooker3, J. Myers4, R. Kudela5, S. Dunagan1, M. Soulage6, J. Livingston7, R. Johnson1, T. Ellis4, N. Clinton4, R. Dominguez4, B. Lobitz8, K. Martin1, E. Fraim4, P. Zell1,
R.Berthold1, C. Smith1, K. Vassigh1, A. Demo1, W. Gore1, and J. Torres9
1NASA Ames Research Center, Moffett Field, CA 94035; 2Biospherical Instruments Inc., San Diego, CA 92110; 3NASA GSFC, MD 20771; 4UC Santa Cruz/NASA, Moffett Field, CA 94035; 5UC Santa Cruz, Santa Cruz, CA, 95064; 6Universities Space Research Association/NASA Ames Research Center, Moffett Field, CA, 94035;
7SRI International/NASA Ames Research Center, Moffett Field, CA 94035; 8Univ. Corporation at Monterey Bay/NASA Ames Research Center, Moffett Field, CA 94035; 9NASA Postdoctoral Program/NASA Ames Research Center, Moffett Field, CA 94035
Abstract
Payload
Imaging Spectrometer
The NASA Coastal and Ocean Airborne Science Testbed (COAST) project advances coastal ecosystems
research and ocean color calibration and validation capability by providing a unique airborne payload optimized
for remote sensing in the optically complex coastal zone. The COAST instrument suite combines a customized
imaging spectrometer, sunphotometer system, and a new bio-optical radiometer package to obtain
ocean/coastal/atmosphere data simultaneously in flight for the first time. The imaging spectrometer (Headwall) is
optimized in the blue region of the spectrum to emphasize remote sensing of marine and freshwater
ecosystems. Simultaneous measurements supporting empirical atmospheric correction of image data is
accomplished using the Ames Airborne Tracking Sunphotometer (AATS-14). Coastal Airborne In situ
Radiometers (C-AIR, Biospherical Instruments, Inc.), developed for COAST for airborne campaigns from fielddeployed microradiometer instrumentation, provide measurements of apparent optical properties at the
land/ocean boundary including optically shallow aquatic ecosystems. Ship-based measurements allowed
validation of airborne measurements. Radiative transfer modeling on in-water measurements from the HyperPro
and Compact-Optical Profiling System (C-OPS, the in-water companion to C-AIR) profiling systems allows for
comparison of airborne and in-situ water leaving radiance measurements. Results of the October 2011 Monterey
Bay COAST mission include preliminary data on coastal ocean color products, coincident spatial and temporal
data on aerosol optical depth and water vapor column content, as well as derived exact water-leaving radiances.
Top: True color composite of the Headwall
imaging spectrometer raw data showing 450nm
(red), 550 (green), and 680 (blue). Pixel
resolution is ~4m from ~6000ft AGL and swath
width is 1.7km.
Insert: Enhanced raw data showing algal
bloom in red.
C-AIR
Line 7
Line 8
Line 9
Line 10
Coastal Airborne In-situ Radiometers (C-AIR)
Scientific Outcomes
• A flight-tested instrument suite suitable for cal/val activities for future satellite missions, as well as currently
operating and developing missions.
• Advanced payload capabilities for airborne carrier platforms including UASs.
• A multi-sensor ocean/atmosphere data set available for improved atmospheric calibration and in-water
algorithms.
• Methodologies for empirical atmospheric correction developed for future airborne imagers of this type (e.g.,
NASA PRISM) when they come online.
• Methods to address the biological properties of important coastal zone ecosystems.
• Enabling technology for a broad range of research activities in the coastal zone to support the scientific
community’s research goals and objectives.
COAST Mission
N
Monterey Bay has both open ocean and optically
complex water masses, so the full dynamic range
of the sensor suite and protocols being used in
the field can be evaluated.
The mission consisted of flying the imaging
spectrometer, together with the AATS-14 and CAIR on the CIRPAS Twin Otter, over an
instrumented surface to evaluate the sensor suite.
The AATS-14 provides a simultaneous empirical
characterization of the atmospheric column (AOD
and water vapor) that will be used for atmospheric
correction.
Three 19-channel microradiometers:
1. with cosine collector for measuring solar
irradiance (Es)
2. Sky radiance (Li) and
3. Total radiance (Lt)
Raw data at 555 nm for global irradiance (Es),
sky radiance (Li) reaching the sea surface, and
radiance from the sea surface, called total
radiance (LT) for four flight lines on Oct. 28,
2011. UTC is +7hrs from local time in October.
Ames Airborne Tracking Sunphotometer (AATS)
Measures:
Solar direct-beam transmission (T) at
14 wavelengths, 353-2139 nm
Spectral range: 320-780 nm with 10 nm
bandwidth to include channels centered
around 412, 443, 490, 510, 555, 665, and
683 nm to match satellite (NASA MODIS)
bands used for ocean color remote
sensing.
Data products:
 Aerosol optical depth (AOD) at 13
channels, 353-2139 nm
 Water vapor column content [using
T(940 nm)]
 Aerosol extinction, 340-2139 nm
 Water vapor density
Physical FOV radiance instrument: 1.25°
half-angle, 0.7° slope angle
The Es and Li radiometers are mounted
within a fairing on top of the aircraft. The Li
radiometer is mounted 40 deg off zenith.
The Lt radiometer is mounted at 40 deg off
nadir alongside the imaging spectrometer.
C-AIR measurements of the downward irradiance (Es), sky
radiance away from the sun (Li) and total surface radiance
(Lt) for each 30 second segment of all flight lines showed
small vari-ances, but were mostly spectrally similar.
Shown are spectra from 30 second segments processed for
glint avoidance by PROSIT along flight line 7, Oct. 28, 2011
at ~6000 ft.
Science Mission October 2011
Ship-based Measurements
During flights, we obtained MODIS Aqua and
Terra, HICO, and MERIS data corresponding to
contemporaneous deployment of the ship-based
measurements from the R/V John Martin (Moss
Landing Marine Lab). Satellite observations will
be used to compare accuracy of radiance
retrievals and derived products versus the
Headwall imaging spectrometer, C-AIR, and the in
situ measurements.
100 ft!
• Underway T, S, Fluorescence
• At each station (2-3 stations per
day):
– Size fractionated chlorophyll,
flow cytometry counts
– CDOM, absorption spectra,
nutrients
– Sunphotometer spectra
– HyperPro cast, C-OPS cast
– Water-leaving radiance,
profile data
– Backscatter/ac-s casts
– ASD surface reflectance
AATS-14
Left: Aerosol optical depths (AOD)
calculated from AATS-14 measurements
for horizontal transects on 28 Oct. at
altitudes 0.024 km ASL (top left) and 1.877
km ASL (bottom left). The AATS-14
channel center wavelengths (in μm) are
given in the legend.
Right: Corresponding mean AOD spectra
(symbols) and log(AOD) vs.
log(wavelength) quadratic fits (dashed
lines) calculated for the total column above
the aircraft for the low (blue) and high (red)
flight legs, and for the layer (green)
bounded by the two altitudes.
Left: Flight path for October 28, 2011. Right: Flight path showing spiral descent from
6000 ft to 100 ft flight lines. Flight planning included timing within +/- 30 min of satellite
overpass.
Science Traceability Matrix
Preliminary Data
A Science Traceability Matrix
provides a project trace from the
science goals to the instrument
requirements and projected
instrument performance. Colored
box outlines indicate the path
through the matrix to meet science
requirements.
Blue: C-OPS
Black: HyperPro II
Red: Headwall
Vertical profiles of columnar water vapor (left), spectral AOD
(middle), and spectral aerosol extinction (right) calculated from
AATS-14 measurements acquired during a spiral descent over
Monterey Bay on 28 October.
Comparison of Headwall (3x3 avg)
reflectance processed using Tafkaa
atmospheric correction, 3 consecutive casts
of C-OPS, and 3 consecutive casts of
HyperPro II for red tide (above) and low
biomass (below) stations. All spectra
matched reasonably well. The C-OPS has
lower variance and less noise at the blue and
red end of the spectrum, but misses the peak
reflectances in red tide waters (above).
Acknowledgements
• Naval Postgraduate School Center for Interdisciplinary Remotely
Piloted Aircraft Systems (CIRPAS) Twin Otter Team.
• UC Santa Cruz and Moss Landing RV John Martin field team.
• UC Davis Spectral Measurements Team: Mui Lay, George Scheer,
and Susan Ustin.
Example of the vertical resolution achieved
by the C-OPS profiler (unbinned reflectance
data for the first 0.5 m of the cast is shown)
COAST Team at NPS CIRPAS in Marina, CA.
Funding: NASA HOPE, Science Mission Directorate, Office of Chief Engineer, and SMD/Earth Science Division