Liane Guild, Brad Lobitz, Randy Berthold, Jeremy KerrBiospheric Science Branch, NASA Ames Research Center, CA

Roy Armstrong, James Goodman University of Puerto Rico at Mayaguez, PR

Collaborators:AVIRIS Team at NASA JPLAirborne Science and Technology Lab at NASA Ames

Funding: Interdisciplinary Research in Earth Science NASA Ocean Biology and Biogeochemistry Program

Contact: Liane.S.Guild@nasa.gov

http://earthscience.arc.nasa.gov/sge/coral-health/

Coral Reef Bleaching and Threats to Biodiversity in Puerto Rico

• Use NASA’s 2005 AVIRIS imagery over La Parguera, Puerto

Rico to map coral reef benthic types and change

• Map the distribution of the threatened Acropora species (A.

cervicornis and A. palmata) along bathymetric zones

• Use AVIRIS data and field measurements to assess the

ecological impact of the 2005 coral bleaching event in

Southwestern Puerto Rico

• Establish permanent reef monitoring transects to track

change

• Improve the interpretation of reef habitat variability and

biodiversity

Objectives

NASA AVIRIS Mission of the 2005 Caribbean Coral Reef Bleaching Event

AVIRIS flight lines over La Parguera, Puerto Rico

• December 12-13, 2005

• Twin Otter Platform, Altitude ~3.5 km

• Pixel Size 2.4 m

• Reef benthic type spectra• Photogrids• GPS• Depth• Water optical properties

Field Measurements

GER spectroradiometer in an underwater housing

Hyperspectral Profiles

Satlantic HyperPro measures:– Lu –upwelling radiance– Ed –downwelling irradiance– Es – surface Ed

Spectral range 350 – 800 nmCalculates Kd (λ) from Ed profilesData obtained during AVIRIS over flights Monthly sampling to address

temporal variability

LiDAR

Bathymetry and reflectivity products ADS Mk II Airborne System April 2006-May 2007 Bathymetry to 50 mSpatial Resolution 4m

Processing Steps

• Atmospheric correction – Tafkaa (Gao et al. 2000, Montes et al. 2001, 2003)• Sun glint removal (Hedley et al. 2005)• Semi-analytical model (Lee et al. 1996, 1998, 1999)• J. Goodman’s implementation of this model

Image Preprocessing

Anomaly Corrections

Glint Removal

Atmospheric Correction

Inversion Model

Semi-Analytical

Input Parameters

Absorption Properties

Bottom Reflectance

Linear Unmixing Model

Inversion Output

Water Constituent Properties

Bottom Albedo (550 nm)

Bathymetry

RMSE

Unmixing Output

Reef, Algae, Sand Distribution

RMSE

Spectral Endmembers

Reef, Algae, Sand

Field Spectra

Forward Model

Semi-Analytical

AVIRIS

2005 AVIRIS: Unmixing Model

J. Goodman (UPRM)

ForwardModel

Preprocessed AVIRIS Imagery

Spectral Input Parameters

Aquatic Absorption Properties

Generic Bottom ReflectanceImage Geometry

Explicit pixel by pixel subsurface angles

View (AVIRIS) Illumination (solar)

Inversion Output

Water Properties

Bathymetry

UnmixingModel

0

0.1

0.2

0.3

0.4

0.5

400 500 600 700Wavelength, nm

Ref

lect

ance Sand

Algae

Coral

Spectral Endmembers

Unmixing Output

Benthic Composition

Sand

AlgaeCoral

Rb = (1/0.54) Rrs (z = a) – (1 – e -2kz) Rw

e -2kz

Rrs (z = a) reflectance just above the water surface

(1/0.54) corrects for transmittance of the air/water interface and the refractive index

Rb is substrate reflectance

k is the attenuation coefficient of the water body

Rw is the water column reflectance in optically deep waters

z is depth (from LiDAR)All terms except z are wavelength specific

Water Column Corrections

R. Armstrong (UPRM)

Effects of Water Column Correction – Sand Target

0

100

200

300

400

500

600

400 450 500 550 600 650 700

Wavelength (nm)

Valu

es

Sand

0

5

10

15

20

25

30

35

40

45

400 450 500 550 600 650 700

Wavelength (nm)

% R

efl

ect

an

ce

Corrected Image

GER

Atmospherically corrected pixel over sand target

In situ percent reflectance of sand target (red line)

AVIRIS water column corrected pixel (blue line)

Depth 2.5 m

Per

cent

Ref

lect

ance

Effects of Water Column Correction - Sea grass Target

0

20

40

60

80

100

120

140

160

180

200

400 450 500 550 600 650 700

Wavelength (nm)

Valu

es

Atmospherically corrected pixel over seagrassesSea grass

0

2

4

6

8

10

12

400 450 500 550 600 650 700

Wavelength (nm)

% R

efl

ect

an

ce

Corrected Image

GER

In situ percent reflectance of sea grass target (red line)

AVIRIS water column corrected pixel (blue line)

Depth 2.5 m

Per

cent

Ref

lect

ance

Effects of Water Column Correction – Coral Target

0

5

10

15

20

25

400 450 500 550 600 650 700

Wavelength (nm)

% R

elf

ecta

nce

Live Coral

0

5

10

15

20

25

400 450 500 550 600 650 700

Wavelength (nm)

% R

efl

ect

an

ce

Corrected Image

GER

Atmospherically corrected pixel over coral target

In situ percent reflectance of typical coral endmember (red line)

AVIRIS water column corrected pixel of mixed living/dead corals and sand(blue line)

Depth 0.5 m

Per

cent

Ref

lect

ance

Temporal Changes in Benthic Composition and Diversity

San Cristobal Reef, La Parguera

Using field transect data from:

August 2005

December 2005

November 2007

24.12

1.29 0.86

46.17

9.38

4.261.14

59.94

21.88

3.12

8.23

3.72

49.29

14.98

22.59

0.00

25.00

50.00

75.00

100.00

Coral Gorgonians Sponges Macroalgae Sand

Cover type

Per

cen

t co

ver

Aug-05 Dec-05 Fall-07

*

*

*

*

**

!

*

Trends in Reef Cover Type

24.12

14.86

9.109.38

0.85 0.003.12

0.05 0.020.00

25.00

50.00

75.00

100.00

Coral (general) Acropora cervicornis Acropora palmata

Cover type

Per

cen

t co

ver

Aug 05 Dec 05 Fall 07

Trends in Coral Cover

Acropora cervicornis (staghorn coral) Transects 2004-2007

20042004 20052005

20062006 20072007

Changes in Biodiversity

Pre-bleaching event (August 2005): 0.70* 0.60**

Post-bleaching and mortality (November 2007): 1.61* 0.22**

* = calculated as each coral species cover as a percent of total coral cover

** = calculated as each coral species cover as a percent of overall cover

Acroporid dominance in 2005, before the bleaching event, was 98%. This dominance diminished to 2% in 2007 accounting for the increase in diversity when only coral species are included in the index calculations. When other reef benthic components (sponges, gorgonians, macroalgae) are taken into account, there was a dramatic decrease in coral diversity according to the Shannon-Wiener Index.

• The Shannon-Wiener Diversity Index is a measurement of biodiversity. • This index takes into account the number of species and the evenness of the species.

Shannon-Wiener Index

Summary AVIRIS data have been atmospherically corrected including:

• Stray-light anomaly suppression

• Removal of sun glint

Unmixing analysis is in progress:

• Using spectral endmembers of coral, sand, and algae

• Analysis performed for depth range 0-10 m

• Use MESMA for unmixing and compare results

Next steps :

• Finish field data analysis for all years

• Implement water column corrections and use of spectral library

• Accuracy assessment of benthic composition classification

• Complete reef degradation and “biodiversity” analysis