NOAA has established the Coastal Ocean Applications and Science Team (COAST) to provide
consensus scientific oversight of the Coastal Waters (CW) Imaging task for the Hyperspectral
Environmental Suite (HES) being developed for GOES-R. The immediate task for COAST is to
review the nominal coastal ocean threshold and goal requirements being used as the basis for the
HES studies. This is the COAST assessment of those requirements and our recommendations for
maximizing the performance and utility of Hyperspectral Environmental Suite Coastal Waters
Imaging HES-CW.
Our primary finding is that if HES-CW is built and operated according to the threshold
requirements as stated in the current Hyperspectral Environmental Suite (HES) Performance and
Operation Requirements Document (PORD) it will provide an excellent new capability for coastal
management and open the door for innovative new science in the coastal ocean. To enhance that
capability we have two types of recommendations. First, we recommend adjustments to the
threshold requirements, which we feel will greatly enhance the value of the HES-CW data. Second,
we recommend some additional goal channels and recommend a prioritization of the goal
requirements in the order that we believe will provide the greatest benefit for the least cost.
The proposed coverage area as shown in Figure 1. does not include the Laurentian Great Lakes. We
believe these are important coastal regions where NOAA has management responsibilities and that
they should be an explicit part of the coverage area imaged every three hours.
Figure 1. The HES-CW coverage area is the U.S. coastal waters Exclusive Economic Zone (EEZ in
Pink) extending approximately 400 km offshore including the EEZ for the state of Hawaii (not
shown). It is recommended that the Laurentian Great lakes (blue) be added to the areas routinely
imaged. Alaska is too far north to be imaged from a geostationary satellite.
The current threshold and goal spectral channels and their planned applications are shown in Table
1. There are a great number of channels from .477 to .550 m and then a gap from .550 to .645 m.
We recommend eliminating the .477 and .763 m channels and replacing them with channels at 580
and 610 nm (20 nm wide) channels. The 580 nm channel is for algal group discrimination and the
610 nm channel is the key channel for detecting suspended sediments, a critical issue for coastal
waters.
Wavelength (m)
Application
0.412 (THRESHOLD)
0.443 (THRESHOLD)
0.477 (THRESHOLD) XXX
0.490 (THRESHOLD)
0.510 (THRESHOLD)
0.530 (THRESHOLD)
0.550 (THRESHOLD)
0.580 new threshold
0.610 new threshold
0.645 (THRESHOLD)
0.667 (THRESHOLD)
0.678 (THRESHOLD)
0.720 new threshold if no 1.00
0.750 (THRESHOLD)
0.763 (THRESHOLD) XXX
Colored dissolved organic Matter (CDOM)
Chlorophyll a, CDOM Particulate Organic Carbon (POC)
Chlorophyll a and Chlorophyll b, O2:O2 dimmer
Chlorophyll a and accessory pigments
Accessory Pigments
Accessory pigments, Suspended sediment
Chlorophyll a, accessory pigments, suspended sediments,
(POC)
Accessory pigments, suspended sediments, water clarity
Suspended sediments, water clarity
Suspended sediments, coccolith concentration
Chlorophyll a, Fluorescence
Chlorophyll a fluorescence
Atmospheric correction, chlorophyll fluorescence
Atmospheric correction
O2 A band
0.865 (THRESHOLD)
0.905 (THRESHOLD) XXX
1.000 new threshold (40 nm)
0.407 to .987 in 10 nm channels
(GOAL)
0.345 new goal (20 nm)
0.380 new goal (20 nm)
1.240 GOAL (40 nm)
1.38 (GOAL)
1.61 (GOAL)
2.26 (GOAL)
11.2 (GOAL)
12.3 (GOAL)
Atmospheric correction, cloud clearing
Column water
Atmospheric Correction
Hyperspectral imaging for discrimination of in-water and
bottom features
Atmospheric correction in coastal waters
CDOM, Atmospheric correction in coastal waters
Atmospheric Correction
Daytime cirrus cloud
Daytime cloud water
Daytime cloud properties
Total water for Sea Surface Temperature (SST)1
Sea Surface Temperature (SST)1
Table 1. HES-CW threshold and goal channels and their applications. The original set of channels
is in CAPS. Recommended new channels are in lower case. It is recommended deleting three of the
original channels indicated by XXX. All channels are at 300 m Ground Sample Distance at the
equator (GSD) with a goal of 150 m GSD except the SST1 channels which have a threshold GSD of
2000 m with a goal GSD of 1000 m.
A key issue for ocean color measurements is accurate calibration and atmospheric correction of the
HES-CW data to obtain water leaving radiances which are used to calculate all of the ocean
products. Good calibration requires accurate pre-launch calibration and characterization of the
sensor and regular on orbit calibration using the moon, a solar diffuser or on-board calibration
source. Additionally, vicarious calibration using accurate water leaving radiances (e.g. from
MOBY) measured at a clear water site is necessary to validate the calibration and atmospheric
correction to provide water leaving radiances to the accuracy needed for ocean color products.
Calibration and atmospheric correction risk reduction activities are planned to prepare for the use of
HES-CW data to produce ocean products beginning soon after the launch of GOES-R.
HES-CW is designed to sample coastal waters. Experience with SeaWiFS and MODIS has shown
that this is more challenging than sampling the open ocean which has been the focus for those
global imagers. In particular there are a greater diversity of water types and atmospheric conditions
in the coastal ocean. For the open ocean the water leaving radiance is assumed to be 0 at
wavelengths longer than .750 m and using this assumption the .750 and .865 m channels are used
to calculate the aerosol radiance. Unfortunately, in coastal waters with high suspended sediments,
or in shallow coastal waters where the bottom is imaged there is significant water leaving radiance
at those wavelengths invalidating that assumption. However, water absorption increases rapidly
with wavelength and in those cases the ocean remains black in longer wavelength channels (1.00,
1.24 and 1.61 m) and those channels can be used for calculating aerosol type and concentration
(Li, et al., 2004). Thus we recommend moving the .905 m channel to 1.000 m. The .905 m
channel is in a water absorption feature and cannot be used for calculating aerosols for atmospheric
correction. If it is not possible to have a channel at 1.000 m then we recommend a channel at .720
m which will be helpful for atmospheric correction and provide an improved baseline for the
chlorophyll fluorescence measurements. We also strongly support the 1.24 and 1.61 m goal
channels for atmospheric correction in coastal waters.
A second challenge for doing atmospheric correction for coastal waters is the presence of absorbing
aerosols offshore from many urban areas. These aerosols absorb particularly strongly in the blue
and UV wavelengths and cannot be accurately corrected using the dark water assumption for longer
wavelengths. Instead it is essential to have one or more wavelengths in the UV and apply a similar
dark pixel assumption to the shortest of those wavelengths. The ideal wavelength is .345 m. A
channel at .380 m can also be used for most waters, but there are occasions when there is
significant water leaving radiance at .380 m, in those cases it can be used to more accurately
quantify the concentration of CDOM. Therefore, we strongly recommend the addition of these goal
channels.
The unique advantage of a geostationary imager is the ability to frequently sample areas of interest.
The threshold sampling of the U. S. EEZ once every three hours with selected sites hourly will be
adequate to resolve the tidal cycles for the critical applications. However, hourly sampling would
greatly enhance many applications. Clouds limit the ability to collect ocean data and hourly
sampling will greatly enhance cloud clearing. Further, to fully resolve the dynamics of certain
coastal phenomenon, for example the vertical migration of some toxic phytoplankton species, will
require more frequent sampling.
A number of studies using airborne imaging spectrometers (hyperspectral imagers) have shown that
having the continuous spectra is of great benefit for resolving coastal features (Lee and Carder,
2001, Lee et al. 2002, Mobley et al., in Press). Multispectral channels (the threshold channels) work
fine for deep water. However when the bottom is imaged, the hyperspectral data are much better for
separating the bottom and water column signatures. The bottom is imaged for 30 km off the west
Florida Coast and over the entire Bahamas Banks. For these and other complex areas hyperspectral
imaging would provide a distinct advantage.
In summary, here is our recommended priority order for the GOAL requirements:
1. More frequent sampling approaching hourly sampling for the entire EEZ and Great Lakes.
2. Add the 1.24, 1.61, .345, .38 m channels for atmospheric correction in coastal waters.
3. Hyperspectral sampling over the 0.4 to 1.0 m spectral range.
4. Higher Signal-to-Noise Ratio (SNR) in all channels, but particularly for .410 m where CDOM
absorption is strong and for wavelengths longer than .750 m used for atmospheric correction.
5. Higher spatial resolution approaching 150 m.
In many cases there is a gradient between the threshold and GOAL requirements. Often the GOAL
requirement will not be achievable, however any significant progress towards the goal is welcome
and will make a valuable contribution. For example, the threshold SNR is 300:1, with a GOAL of
900:1. However, an instrument with a SNR of 600:1 will provide superior performance to one that
just meets the threshold, and credit should be given for this enhanced performance.
In summary, HES-CW build to the threshold requirements will be a powerful new tool for
managing the coastal ocean. We specifically recommend changing the wavelengths for three
threshold channels which will greatly improve the performance without incurring significant cost.
We recommend two additional goal channels in the UV to improve atmospheric correction in the
coastal regions near urban and industrial areas. We recommend a priority order for the GOAL
requirements. We recommend that credit be given for significant progress towards a goal even
though the actual goal is not achieved.
References
Lee, Z. P., K. L. Carder, R. F. Chen, and T. G. Peacock, “Properties of the water column and
bottom derived from Airborne Visible Infrared Imaging Spectrometer (AVIRIS) data”, J. Geophys.
Research, 106(C6), 11,639-11,651, 2001.
Lee, Z. P., and K. L. Carder, “Effects of spectral-band number on retrievals of water column and
bottom properties from ocean-color data”, Appl. Opt., 41, 2191-2201, 2002.
Mobley, C. D., L. K. Sundman, C. O. Davis, T. V. Downes, R. A. Leathers, M. J. Montes and J. H.
Bowles, 2005, Interpretation of hyperspectral remote-sensing imagery via spectrum matching and
look-up tables, Appl. Opt., 44(17), 3576-3592.