High resolution mapping of tropical mangrove ecosystems using hyperspectral and radar remote sensing

Abstract

Mangrove ecosystems are in serious decline around the world and various initiatives are underway to assess their current coverage and loss in cover. These ecosystems occur as thin strips along coastlines or rivers and, due to the strong environmental gradients present, mangroves show high spatial variability along short transects. Remote sensing tools that offer high spatial resolution mapping and high information content are needed to provide good differentiation of the various mangrove zones and types. The added complexities of tropical atmospheric conditions provide further challenges in terms of the selection of sensors and image analysis methodologies. This paper explores the possibility of combining a high spatial/spectral resolution scanner, 'Compact Airborne Spectrographic Imager' (CASI), with the airborne National Aeronautics & Space Administration's polarimetric radar, 'AIRSAR', for mapping and monitoring of mangrove estuaries. The Daintree River estuary in far North Queensland, Australia was chosen for this study due to its diversity of mangrove species. Imagery acquired by both the CASI airborne scanner (14 bands, 2.5 m pixel) and the AIRSAR (L-and P-band polarimetry, C-band interferometry, 10 m pixel) has been used to produce detailed maps of the mangrove zones in the estuary.The advantages and difficulties associated with multi-source data integration are investigated in this paper. While radar provides general structural information in relation to mangrove zonation, high-resolution hyperspectral scanners allow for finer-detailed analysis and green-biomass information. Classifications (maximum likelihood) of both the individual and integrated datasets are performed, with the latter producing more accurate results. Application of a hierarchical neural network classification is also explored, where the more general mangrove zones are separated first based on structural information, then species or specie-complexes are extracted in subsequent levels using spectral differences.

Separating Mangrove Species and Conditions Using Laboratory Hyperspectral Data: A Case Study of a Degraded Mangrove Forest of the Mexican Pacific

“…To date, there have been several examples of applications of hyperspectral images on mangrove forests. Airborne hyperspectral instruments, such as Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) (e.g., [11]), Compact Airborne Spectrographic Imager (CASI) [12][13][14] and Airborne Imaging Spectrometer for Application (AISA+) [15], and satellite hyperspectral imagery (Hyperion) (e.g., [16,17]) have been used for monitoring and classifying mangrove species. The results from these studies would suggest that classifications based on hyperspectral imagery can provide satisfactory results for mapping mangrove communities.…”

Natural and anthropogenic changes to mangrove distributions in the Pioneer River Estuary (QLD, Australia)

“…IKONOS, Quickbird; Wang et al 2004) and high spatial resolution hyperspectral data integrated with radar (e.g. CASI and AIRSAR; Held et al 2003), each of which offers advantages in high diversity mangrove ecosystems. Radar has proven valuable for discrimination of degraded mangroves (open canopy) from intact forest (closed canopy) based on increased backscatter from C-, L-and P-band frequencies (Proisy et al 2002), and its integration with optical data should improve dieback classifications.…”

Discrimination of Tropical Mangroves at the Species Level with EO-1 Hyperion Data

“…It is evident that conventional remote sensing instruments are now operationally used for mapping and monitoring mangroves at the broad level [31][32][33][34][35][36][37][38][39][40][41]. However, the spatial and spectral information provided by this conventional equipment may not be sufficient for studying mangrove ecosystems and their diversity in details [14,23,26,31,35,[42][43][44][45][46]. As a result, new generation sensors that possess higher spatial and spectral resolutions are therefore needed for a finer level of mangrove studies [17,35,42,43,[45][46][47].…”

“…Earth Observation remote sensing has been recognized as a powerful tool for this purpose [23,[25][26][27][28][29][30]. It is evident that conventional remote sensing instruments are now operationally used for mapping and monitoring mangroves at the broad level [31][32][33][34][35][36][37][38][39][40][41].…”