Sea ice thickness retrieval algorithms based on in situ surface elevation and thickness values for application to altimetry

In situ measurements of sea ice thickness ( I ), snow depth ( S ), and snow freeboard ( F sn ) from drilling profile lines from 15 cruises into the Southern Ocean, Antarctica, were analyzed. I was calculated from in situ F sn and S using an isostatic approach. I was also directly estimated from F sn as can be obtained from laser altimetry. The root‐mean‐square difference (RMSD) between observed and calculated I reduces, and the correlation between F sn and I increases substantially, when (1) using values averaged over the survey lines (∼50 m) instead of single drill hole measurements (∼1 m) and (2) treating positive and negative sea ice freeboard ( F i ) separately. For small F i , however, S approximates F sn pointing toward an isostatic balance also between S and I . Our linear regression analysis between the in situ measurements suggests a direct conversion of F sn into I using a region‐specific set of equations. RMSD values are similar to those obtained employing isostatic balance models and treating positive and negative F i separately. However, more data would have been needed to obtain significant differences between most of the various models suggested. Still our new approach gives a viable alternative for Antarctic I retrieval from altimetric measurements of F sn alone. Correlation between in situ observations of F sn and S is high. RMSD between observed and calculated S is small. This suggests estimation of S from altimetric F sn measurements. Such S has an estimated precision of ∼5 cm, and is neither affected by snow wetness or grain size nor limited to S < 50 cm.