Vegetation Height and Structure - Derived from ALOS-1 PALSAR, Landsat and ICESat/GLAS, Australia Coverage

Australia has historically used structural descriptors of height and cover to characterize, differentiate, and map the distribution of woody vegetation across the continent but no national satellite-based structural classification has been available. In this study, we present a new 30 m spatial resolution reference map of Australian forest and woodland structure (height and cover), with this generated by integrating Landsat Thematic Mapper (TM) and Enhanced TM, Advanced Land Observing Satellite (ALOS) Phased Arrayed L-band Synthetic Aperture Radar (PALSAR) and Ice, Cloud, and land Elevation (ICESat), and Geoscience Laser Altimeter System (GLAS) data. ALOS PALSAR and Landsat-derived Foliage Projective Cover (FPC) were used to segment and classify the Australian landscape. Then, from intersecting ICESat waveform data, vertical foliage profiles and height metrics (e.g. 95% percentile height, mean height and the height to maximum vegetation density) were extracted for each of the classes generated. Within each class, and for selected areas, the variability in ICESat profiles was found to be similar with differences between segments of the same class attributed largely to clearance or disturbance events. ICESat metrics and profiles were then assigned to all remaining segments across Australia with the same class allocation. Validation against airborne LiDAR for a range of forest structural types indicated a high degree of correspondence in estimated height measures. On this basis, a map of vegetation height was generated at a national level and was combined with estimates of cover to produce a revised structural classification based on the scheme of the Australian National Vegetation Information System (NVIS). The benefits of integrating the three datasets for segmenting and classifying the landscape and retrieving biophysical attributes was highlighted with this leading the way for future mapping using ALOS-2 PALSAR-2, Landsat/Sentinel-2, Global Ecosystem Dynamics Investigation (GEDI), and ICESat-2 LiDAR data.

Data Creation

Supplemental Information Filenames for these products conforms to the AusCover standard naming convention. The standard form of this convention is:

HEIGHT TIF PRODUCTS (percentile heights are the height where that percentage of plant material has been intercepted within a cluster, where a cluster is a group of similar segments):

• alpsbk_aust_y2009_sd1a2.tif - Height where 25% of the plant cover has been intercepted (DN=decimetres+1; unsigned 16 bit; null=0)
• alpsbk_aust_y2009_sd2a2.tif - Height where 50% of the plant cover has been intercepted (DN=decimetres+1; unsigned 16 bit; null=0)
• alpsbk_aust_y2009_sd3a2.tif - Height where 75% of the plant cover has been intercepted (DN=decimetres+1; unsigned 16 bit; null=0)
• alpsbk_aust_y2009_sd4a2.tif - Height where 95% of the plant cover has been intercepted (DN=decimetres+1; unsigned 16 bit; null=0)
• alpsbk_aust_y2009_sd5a2.tif - Height of peak plant cover density (DN=decimetres+1; unsigned 16 bit; null=0)

PLANT COVER TIF PRODUCTS (Defined as 1 - gap fraction):

• alpsbk_aust_y2009_se1a2.tif - Fraction of plant cover below 5 m (DN=percentage*100+1; unsigned 16 bit; null=0)
• alpsbk_aust_y2009_se2a2.tif - Fraction of plant cover between 5 m and 10 m (DN=percentage*100+1; unsigned 16 bit; null=0)
• alpsbk_aust_y2009_se3a2.tif - Fraction of plant cover between 10 m and 30 m (DN=percentage*100+1; unsigned 16 bit; null=0)
• alpsbk_aust_y2009_se4a2.tif - Fraction of plant cover above 30 m (DN=percentage*100+1; unsigned 16 bit; null=0)
• alpsbk_aust_y2009_se5a2.tif - Total plant cover fraction (DN=percentage*100+1; unsigned 16 bit; null=0)

STRUCTURE TIF PRODUCT (Categorical data):

• alpsbk_aust_y2009_sf1a2.tif - Forest structure codes derived from alpsbk_aust_y2009_sd4a2.tif
• alpsbk_aust_y2009_se5a2.tif using a version of the Walker and Hopkins (1990) structural classification Code Structural Formation Total plant cover fraction 95^th percentile height:
  • 0 No Data
  • 10 No trees 0%
  • 21 Low scattered trees 0% to 6% <9 m
  • 22 Medium scattered trees 0% to 6% 9 m to 17 m
  • 31 Low open woodland 6% to 11% <9 m
  • 32 Medium open woodland 6% to 11% 9 m to 17 m
  • 33 Tall open woodland 6% to 11% 17 m to 27 m
  • 41 Low woodland 11% to 30% <9 m
  • 42 Medium woodland 11% to 30% 9 m to 17 m
  • 43 Tall woodland 11% to 30% 17 m to 27 m
  • 44 Very tall woodland 11% to 30% 27 m to 57 m
  • 51 Low open forest 30% to 70% <9 m
  • 52 Medium open forest 30% to 70% 9 m to 17 m
  • 53 Tall open forest 30% to 70% 17 m to 27 m
  • 54 Very tall open forest 30% to 70% 27 m to 57 m
  • 55 Extremely tall open forest 30% to 70% >57 m
  • 63 Tall closed forest >70% 17 m to 27 m
  • 64 Very tall closed forest >70% 27 m to 57 m

ALOS PALSAR L-band Fine Beam Dual (HH and HV) polarisation data mosaics at 25 m spatial resolution, provided through the JAXA K&C Initiative, were combined with an Australian mosaic of persistent green vegetation cover derived from Landsat sensor time-series data (Department of Environment and Science, Queensland Government, 2022). These data were segmented to map clumps of contiguous vegetation structure and reduced to a maximum of 1000 unique classes using k-means based cluster analysis. These classes were then intersected with ICESat/GLAS L2 (Release 33) Global Land Surface Altimetry Data (GLA14) data acquired between 2003 and 2009 and obtained from the National Snow and Ice Data Centre (NSIDC). All GLAS laser shots were corrected for differences in footprint size, laser output power, vegetation/ground reflectance, and terrain slope. These laser shots were aggregated for each cluster and processed to mean vertical profiles of P_gap (θ,z). Vertical plant profiles were then derived and height of peak foliage density (Hpeak) and height percentiles (95^th, 75^th, 50^th, and 25^th) extracted. To produce a national map, each clump in the original segmentation was then assigned the mean vertical profile corresponding to the nearest cluster centroid.