@article{PAR00014087,
  title = {{E}valuation of spaceborne {L}-band radiometer measurements for terrestrial freeze/thaw retrievals in {C}anada},
  author = {{R}oy, {A}. and {R}oyer, {A}. and {D}erksen, {C}. and {B}rucker, {L}. and {L}anglois, {A}. and {M}ialon, {A}. and {K}err, {Y}ann},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he landscape freeze/thaw ({F}/{T}) state has an important impact on the surface energy balance, carbon fluxes, and hydrologic processes; the timing of spring melt is linked to active layer dynamics in permafrost areas. {L}-band (1.4 {GH}z) microwave emission could allow the monitoring of surface state dynamics due to its sensitivity to the pronounced permittivity difference between frozen and thawed soil. {T}he aim of this paper is to evaluate the performance of both {A}quarius and soil moisture and ocean salinity ({SMOS}) {L}-band passive microwave measurements using a polarization ratio ({PR})-based algorithm for landscape {F}/{T} monitoring. {W}eekly {L}-band satellite observations are compared with a large set of reference data at 48 sites across {C}anada spanning three environments: 1) tundra; 2) boreal forest; and 3) prairies. {T}he reference data include in situ measurements of soil temperature ({T}-soil) and air temperature ({T}-air), and moderate resolution imaging spectroradiometer ({MODIS}) land surface temperature ({LST}) and snow cover area ({SCA}) products. {R}esults show generally good agreement between {L}-band {F}/{T} detection and the surface state estimated from four reference datasets. {T}he best apparent accuracies for all seasons are obtained using {T}-air as the reference. {A}quarius radiometer 2 (incidence angle of 39.6 degrees) data give the best accuracies (90.8%), while for {SMOS}, using the {A}quarius temporal characteristics, the best results (87.8% of accuracy) are obtained at higher incidence angles (55 degrees-60 degrees). {T}he {F}/{T} algorithm identifies both freeze onset and end with a delay of about 1 week in tundra and 2 weeks in forest and prairies, when compared to {T}-air. {T}he analysis shows a stronger {F}/{T} signal at tundra sites due to the typically clean transitions between consistently frozen and thawed conditions (and vice versa) and the absence of surface vegetation. {R}esults in the prairies were poorer because of the influence of vegetation growth in summer (which decreases the {PR}) and the high frequency of ephemeral thaw events during winter. {F}reeze onset and end maps created from the same algorithm applied to {SMOS} and {A}quarius measurements characterize similar {F}/{T} patterns over {C}anada. {T}his study shows the potential of using {L}-band spaceborne observations for {F}/{T} monitoring, but underlines some limitations due to ice crusts in the snowpack, liquid water content in snow cover during the spring freeze to thaw transition, and vegetation growth.},
  keywords = {{A}quarius ; {C}anada ; freeze/thaw ; passive microwave ; polarization ratio ; {SMOS} ; {CANADA}},
  booktitle = {},
  journal = {{IEEE} {J}ournal of {S}elected {T}opics in {A}pplied {E}arth {O}bservations and {R}emote {S}ensing},
  volume = {8},
  numero = {9},
  pages = {4442--4459},
  ISSN = {1939-1404},
  year = {2015},
  DOI = {10.1109/jstars.2015.2476358},
  URL = {https://www.documentation.ird.fr/hor/{PAR}00014087},
}