In case anyone finds it useful when decoding recon data and trying to get an estimate for what it means at the surface, here's a table of dropsonde conversion factors based off of various heights. Just multiply the observed wind at that height and you'll get a surface observation. Note that these are the mean conversion factors; not all hurricanes will fit this mean profile and there are extreme cases where the standard conversion ratios can be off by 10-20% in either direction. Low-level invests are typically flown around 1000ft or 850mb; normal recon flights are flown around 700mb.

The graph which this is based off of may be found at http://www.nhc.noaa.gov/aboutwindprofile.shtml.

For the eyewall/inner core...
700mb -- 0.91
3000m -- 0.98
2500m -- 1.04
2000m -- 1.06
1500m -- 1.10
850mb -- about 1.12
1000m -- 1.16
500m -- 1.21
1000ft -- 1.20

In the outer vortex, these conversion factors become...
700mb -- 0.78
3000m -- 1.01
2500m -- 1.04
2000m -- 1.05
1500m -- 1.08
850mb -- about 1.08
1000m -- 1.09
500m -- 1.04
1000ft -- 1.00