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<p>Satellite radar backscatter contains unique information on land surface moisture, vegetation features, and surface roughness and has thus been used in a range of Earth science disciplines. However, there is no single global radar data set that has a relatively long wavelength and a decades-long time span. We here provide the first long-term (since 1992), high-resolution (<span class="inline-formula">∼8.9</span> km instead of the commonly used <span class="inline-formula">∼25</span> km resolution) monthly satellite radar backscatter data set over global land areas, called the long-term, high-resolution scatterometer (LHScat) data set, by fusing signals from the European Remote Sensing satellite (ERS; 1992–2001; C-band; 5.3 GHz), Quick Scatterometer (QSCAT, 1999–2009; Ku-band; 13.4 GHz), and the Advanced SCATterometer (ASCAT; since 2007; C-band; 5.255 GHz). The 6-year data gap between C-band ERS and ASCAT<span id="page1578"/> was filled by modelling a substitute C-band signal during 1999–2009 from Ku-band QSCAT signals and climatic information. To this end, we first rescaled the signals from different sensors, pixel by pixel. We then corrected the monthly signal differences between the C-band and the scaled Ku-band signals by modelling the signal differences from climatic variables (i.e. monthly precipitation, skin temperature, and snow depth) using decision tree regression.</p> <p>The quality of the merged radar signal was assessed by computing the Pearson <span class="inline-formula"><i>r</i></span>, root mean square error (RMSE), and relative RMSE (rRMSE) between the C-band and the corrected Ku-band signals in the overlapping years (1999–2001 and 2007–2009). We obtained high Pearson <span class="inline-formula"><i>r</i></span> values and low RMSE values at both the regional (<span class="inline-formula"><i>r</i>≥0.92</span>, RMSE <span class="inline-formula">≤</span> 0.11 dB, and rRMSE <span class="inline-formula">≤</span> 0.38) and pixel levels (median <span class="inline-formula"><i>r</i></span> across pixels <span class="inline-formula">≥</span> 0.64, median RMSE <span class="inline-formula">≤</span> 0.34 dB, and median rRMSE <span class="inline-formula">≤</span> 0.88), suggesting high accuracy for the data-merging procedure. The merged radar signals were then validated against the European Space Agency (ESA) ERS-2 data, which provide observations for a subset of global pixels until 2011, even after the failure of on-board gyroscopes in 2001. We found highly concordant monthly dynamics between the merged radar signals and the ESA ERS-2 signals, with regional Pearson <span class="inline-formula"><i>r</i></span> values ranging from 0.79 to 0.98. These results showed that our merged radar data have a consistent C-band signal dynamic.</p> <p>The LHScat data set (<a href="https://doi.org/10.6084/m9.figshare.20407857">https://doi.org/10.6084/m9.figshare.20407857</a>; Tao et al., 2023) is expected to advance our understanding of the long-term changes in, e.g., global vegetation and soil moisture with a high spatial resolution. The data set will be updated on a regular basis to include the latest images acquired by ASCAT and to include even higher spatial and temporal resolutions.</p>