Comparison of Multispectral and Hyperspectral Signatures of Coral Reef Substrate by Ankita Acharya

Comparison of Multispectral and Hyperspectral Signatures of Coral Reef Substrate



Ankita Acharya (MG-0109)

Guide:

Nandini Ray Chaudhury Sci/ Engr-SD. END/ABHG/EPSA. SAC (ISRO)

Introduction 



Coral Reefs  Marine ecosystem  Coral polyps + zooxanthallae  *Temperature 220C to 280C, not < 150C  *Depth 50 m (shallow); 100 m  *Salinity 32-40 ppt  *Found 300N and 300S latitude Importance  Storage bank  Food  Medicine  Protect coast  Habitat/ nursery  Feed area  Fishing  Tourism * source: Encyclopedia Britanica

Cont... • Threats • Sea water temperature • Sea water transperancy •Run off sediments • Pollutants

• Population pressure • Multispectral and Hyperspectral •The term "multi" is derived from the Latin word for "many" and "hyper" is the Greek word for "over", "above", or an "exaggerated amount". The science of multispectral and hyperspectral remote sensing is based on taking a portion of the electromagnetic spectrum and dividing it into number of bands for the purpose of analytical computation.

Aim 

Pixel level Comparison of Multispectral and Hyperspectral Signatures of Coral Reef Substrates.

Objective    

To generate a reef specific classification system to build a theoritical approach.

Generation of spectral signatures of selected coral reefs using multispectral data. Generation of spectral signatures of selected coral reefs using hyperspectral data To compare multispectral and hyperspectral signatures of coral reef substrates.

Data Used Multispectral

Hyperspectral



RESOURCESAT-1 (IRS-P6)



Earth Observation – 1



LISS-III



Hyperion

LISS-III sensor

Hyperion Sensor

Comparison of Two Sensors LISS-III

Hyperion

Platform

Resourcesat

EO1

Orbital altitude

817 km

705 km

Swath

141 km

7.5 km

Swath width

140 km

7.7 km

Spatial resolution

23.5 m

30 m

Repetivity

24 days

Data aquisition as per request

Revisit time

5 days

Data aquisition as per request

Spectral resolution (no. of bands with bandwidth)

520-590 nm 620-680 nm 770-860 nm 1550-1700 nm

10 nm 400-2500 nm 220

Radiometric resolution

7 bit

16 bit

Kind of sensor (Spatial scanning technique)

Pushbroom

Methodology Multispectral

Hyperspectral

Preprocessing

• Data Downloading

• FCC Generation

• Radiance conversion

• Subsetting

• Enhancement

Data generation

Data generation • AOI

• AOI

• ROI

• ACII

Comparison

5 3 4

1. Gulf of Kachchh 2. Malvan 3. Lakshadweep 4. Gulf of Mannar 5. Andaman 6. Nicobar

Rationale Comparison of Indian Coral Reef Regions: Inter and Intra Reef Classes Reef Regions

Reef Type

Geomorphological Zone

Geomorphological Sub Zone

Ecological Zone

Total

Gulf of Kachchh

Malvan

Lakshadweep

Gulf of Mannar

Andaman

Nicobar

Interview island Port Mount viewed from IRS P6 - LISS-III

North

Port Mount Bay

South

Malay island Interview island viewed from IRS P6 - LISS-III showing north and south study area

Test sites

Malay island viewed from IRS P6 - LISS-III

Classification Scheme for Coral Reef Habitat Level-1

Level-2

Biogeographic region

Reef Type

Indo-west Pacific Faunal Province

Fringing Reef

Level-3

Level-4

Geomorphological Zone

Geomorphological sub zone

Reef Front Reef Slope (Deeper) Reef Slope Reef Crest Moat Reef Flat Bare Reef Flat Sanded Reef Flat Benthic Sub Zone Depression Zone on the Reef Flat Sand Patch Sand Vegetation Beach Dry Sand Sand with overlaying water column

Results

Data Source: IRS-P6 LISS-III Dated: 22 February 2004

Data Source: EO1 Hyperion Dated: 2004

Port Mount Bay

Interview North

Interview south

Conclusion 



Hyperspectral data enhances the potential of substrate level discrimination of coral reef targets. Higher in spectral Channel 2 (Green band: 520-590nm) and 3 (Red Band : 620-680 nm).



A secondary peak response of the substrates is observed for all pixel groups in between 1000 to 2000 nm in the hyperspectral signatures which is not present for the multi-spectral data. Hyperspectral data thus helps to understand the substrate response in the infra-red region of the spectrum which becomes difficult in the multi-spectral data because of point data in two discrete spectral channels representing NIR and SWIR regions. Sand in general gives the highest spectral response in the entire spectrum

References                                     

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