Nguyen Huu Huan, Tong Phuoc Hoang Son and Lau Va Khin

Dr. Nguyen Huu Huan 1 , Tong Phuoc Hoang Son 2 and Lau Va Khin 3

1 Head of Department of Marine Ecology, InsƟ tute of Oceanography, Vietnam Wikipage: hƩ p://www.nf-pogo-alumni.org/~Elisee+Toualy 1 Senior Researcher, InsƟ tute of Oceanography, Vietnam Wikipage: hƩ p://www.nf-pogo-alumni.org/~Tong+Phuoc+Hoang+Son 1 Senior Researcher, InsƟ tute of Oceanography, Vietnam Wikipage: hƩ p://www.nf-pogo-alumni.org/~Va+Khin+Lau

ApplicaƟ on of remote sensing technology in the mapping coral reefs and seagrass beds in the coastal waters of Ninh Thuan and Binh Thuan provinces

IntroducƟ on

Remote sensing technology plays a very important role for observing the Earth’s surface. Knowing the importance of remote sensing techniques in environmental observaƟ on and monitoring, Vietnam launched the VNREDSAT-1 satellite (Vietnam Natural Resources, Environment & Diaster – monitoring Satellite-1), the 7 th May 2013. The VNREDSAT-1 system comprises an opƟ cal satellite capable of capturing images with a resoluƟ on of 2.5 metres for PanchromaƟ c type, 10 m resoluƟ on for mulƟ spectral images. This satellite aims to monitor and study natural resources and the environment as to fi nd suitable soluƟ ons to prevent natural disasters, and as to opƟ mise the management of natural resources. Ninh Thuan-Binh Thuan coastal area is located in upwelling region, which provides fi shing grounds for many marine organisms of economic value. Importantly, this is also the area in which the fi rst two nuclear power plants in Vietnam will be built. Thus, monitoring and warning systems to avert of changes in the environment and natural resources under socioeconomic pressure are essenƟ al. This can only be saƟ sfi ed by the use of remote sensing data, including VNREDSat-1 images. This paper will present some preliminary results on mapping coral reefs and seagrass beds in the coastal waters of Ninh Thuan and Binh Thuan provinces from the Vietnam naƟ onal project: “Building the Dataset on Oceanography Parameters from VNREDSAT-1 and Other Satellite Imageries in Coastal Waters of Ninh Thuan and Binh Thuan Provinces for Sustainable Economic Development”.

Study Area

The coastal waters of Ninh Thuan – Binh Thuan (Figure 1) is located in the south of Vietnam. The area covers strong upwelling waters as well as typical coral reefs and seagrass beds, which are mainly living on mixing boƩ om types of sand, death coral and rock in the range of about 1.5 km from the coastline. In recent years, following the requirement of economic developing, a new road along the coast was opened and connected to the No. 1 naƟ onal road to the North. This development is increasing the threat to the coastal ecosystems, directly and indirectly, for both coral reefs and sea

Data Satellite data

A satellite image of VNREDSAT1 (V130904033142X_2A code, level 2A, date Agency and used in this study. This image includes 4 spectral bands (red, and very good quality (i.e. 0% cloud cover level). grass beds in this study area.

Figure 1 - The studied area scope and 321 color composite VNREDSAT1 image (V130904033142X_2A )

Figure 2 - Some images

04 Sep 2013) is acquired from the (Vietnamese) NaƟ onal Remote Sensing green, blue and infrared), 10 m spaƟ al resoluƟ on, 8 bit radiance resoluƟ on, of fi eldwork

In situ data

A total of 292 ground control points of 11 substrate types were observed using a small boat (diving/snorkeling) as well as walking on Ɵ dal ground at low Ɵ dal level from 27 th to 30 th September 2014 (Figures 1 and 2). There are 66 points of low-density seagrass, 61 points of high-density seagrass, 31 points of hard coral, 48 points of death coral/rock/algae and 51 points of sand/

low-density life coral substrates. At each data point, the cover level was measured using a quadrant frame (50 x 50 cm). AddiƟ onally a photo was taken by using a Pentax OpƟ on WG2 digital camera and track locaƟ on posiƟ on by Garmin GPSMAP 76CSx with projecƟ on of UTM-WGS84 zone 49N. We also divided random surveyed data into two datasets, one including 146 GCPs for detecƟ on and another one including 146 GCPs for error assessment. The ground control points of eleven substrates for detecƟ on underwater habitats are shown in Figure 3.

A survey for measuring the depth and taking sediment samples in Figure 3 - The ground control points of 11 substrates used for detecƟ on of underwater habicoastal waters of Ninh Hai region tats in coastal waters of Ninh Thuan province was also carried out at the same Ɵ me (i.e. September 2014).

Data processing

Several prepossessing steps were applied for underwater habitat mapping in Ninh Hai –Ninh Thuan waters, which include radiometric calibraƟ on, solar gliƩ er removing, atmospheric correcƟ on, water column correcƟ on (i.e. BoƩ om Refl ectance Index (BRI) and Depth Invariant Index (DII) method), and classifi caƟ on. The BRI was esƟ mated based on light aƩ enuaƟ on ability in diff erent depths (see Figure 4). In contrast, the DII uses two bands to reduce the water depth parameter: , in which k i /k j is the raƟ o of slope of band i and band j in natural logarithm scale in homogenous sandy points in diff erent depths (Figure 4). )()( sij j i siiij LLLn k k LLLnDII 

Figure 4 - The fl ow chart for sea-grass mapping by remote sensing techniques base on BRI and DII methods

Results and Discussion

The classifi caƟ on results for both BRI and DII are showed in more detail in Figure 5. The BRI method gives a relaƟ ve good accuracy of 64.47% and a Kappa coeffi cient of 0.48. Whereas, the DII method gave a beƩ er accuracy of 72.38% and a Kappa coeffi cient of 0.56. To the current date, these are only preliminary results and tesƟ ng for habitat mapping in an area of coastal shallow waters of the Ninh Thuan province. In future studies we will conƟ nue to carry out underwater habitat mapping in others areas of Ninh Thuan – Binh Thuan provinces. We are confi dent that the accuracy level of classifi caƟ ons will improve, if we rearrange and declass the model as to beƩ er fi t the real date.