@article{fdi:010086659,
  title = {{Q}uantifying the sensitivity of {L}-{B}and {SAR} to a decade of vegetation structure changes in savannas},
  author = {{W}essels, {K}. and {L}i, {X}. {X}. and {B}ouvet, {A}lexandre and {M}athieu, {R}. and {M}ain, {R}. and {N}aidoo, {L}. and {E}rasmus, {B}. and {A}sner, {G}. {P}.},
  editor = {},
  language = {{ENG}},
  abstract = {{G}lobal savannas are the third largest carbon sink with large human populations being highly dependent on their ecosystem services. {H}owever, savannas are changing rapidly due to climate change, fire, animal management, and intense fuelwood harvesting. {I}n southern {A}frica, large trees (>5 m in height) are under threat while shrub cover (<3 m) is increasing. {T}he collection of multi-date airborne {L}i{DAR} ({ALS}) data, initiated over a decade ago in the {L}owveld of {S}outh {A}frica, provided a rare opportunity to quantify the ability of {L}-band {SAR} to track changes in savanna vegetation structure and this study is the first to do so, to our knowledge. {T}he objective was to test the ability of {ALOS} {PALSAR} 1&2, dual-pol ({HH}, {HV}) data to quantify woody cover and volume change in savannas over 2-, 8-and 10-year periods through comparison to {ALS}. {F}or each epoch (2008, 2010, 2018), multiple {PALSAR} images were processed to {G}amma0 (gamma 0) at 15 m resolution with multi-temporal speckle filtering. {ALS} data were processed to fractional canopy cover and volume, and then compared to 5 x 5 aggregated (75 m) {SAR} mean gamma 0. {T}he {ALS} cover change ({D}elta {CALS}) and volume change between pairs of years were highly correlated, with ({R}2 > 0.8), thus results for cover change applied equally to volume change. {C}over change was predicted using (i) direct backscatter change or (ii) the difference between annual cover map product derived using the {B}ayesian {W}ater {C}loud {M}odel ({BWCM}) and logarithmic models. {T}he linear relationship between {D}elta gamma 0 and {D}elta {CALS} varied between year pairs but reached a maximum {R}2 of 0.7 for 2018-2010 and a moderate {R}2 of 0.4 for 2018-2008. {O}verall, 1 d{B} {D}elta gamma 0 corresponded to approximately 0.1 cover change. {T}he three cover change models had very similar uncertainties with mean {RMSE} = 0.15, which is 13% of the observed cover change range (-0.6 to +0.6). {T}he direct backscatter change approach had less underestimation of positive and negative cover change. {T}he {L} -band backscatter had a higher sensitivity than suggested by previous studies, as it was able to reliably distinguish cover change at 0.25 increments. {T}he {SAR}-derived cover change maps detected the loss of stands of big trees, and widespread increases in cover of 0.35-0.65 in communal rangelands due to shrub encroachment. {I}n contrast, the maps suggest that cover generally decreased in conservation areas, forming distinct fence-line effects, potentially caused by significant increases in elephant numbers and frequent, intense wildfires in reserves.},
  keywords = {{SAR} ; {S}avannas ; {L} -{B}and ; {L}i{DAR} ; {V}egetation structure ; {ALOS} {PALSAR} ; {S}outh {A}frica ; {AFRIQUE} {DU} {SUD}},
  booktitle = {},
  journal = {{R}emote {S}ensing of {E}nvironment},
  volume = {284},
  numero = {},
  pages = {113369 [21 p.]},
  ISSN = {0034-4257},
  year = {2023},
  DOI = {10.1016/j.rse.2022.113369},
  URL = {https://www.documentation.ird.fr/hor/fdi:010086659},
}