Vlacq

D= 91 km
Center: 54¡S, 39¡E

Count Area: 1615 km^2
Observed Density (@ 1km): 27900 ± 4200
Age: 3.9 ± 0.1 (+sec: 4.0)
Stoffler epoch: Nectarian
Fit density: 35900 ± 5600
PF fit: good, smallest slightly shallow

Age calculation notes:
- good fit. fit improved using Hausen and Holsapple scaling hard rock with a strength of Y=2e7 (SM).
- OK fit - a little off for small craters (shallow) - perhaps it can be improved by using strength scaling law; adding OSs slightly degrades fit and changes age. Using Hausen & Holsapple strength scaling (SN) improves fit, but does not change age (MRK).
- why does using HH scaling work (i.e., including strength)? Including strength causes the PF to become shallower for small craters (transition occurs ~ 1.5 km), which is why the fit is better. But is there justification for using this law here and not with other craters (i.e., is geology different)? No particular reason to think this surface should be stronger than other craters - has a weathered appearance. But the transition is at a relatively small D, so perhaps the strength change isn't going to be visible. (MRK)

USGS geology: 
Crater mapped as Nectarian (pre-Imbrian is their term?). Portions of crater floor mapped as fill (volcanic?) with an Imbrian age - some may be original floor (excluded?).

Wilhelms: 
Pre-Nectarian (all materials)

Floor material: 
Best guess is not original (at least for section counted). Smooth flat floor, edges meeting wall look embayed, few filled larger craters. Also surrounded by a few craters filled. Material looks not quite fresh. Thin layer of soft over hard?

Geology Observations: 
Ejecta blanket very eroded. Rim looks eroded, but still a little sharpness. Small central peak - looks eroded. Portion of floor flat, but remaining is hummocky (original floor, collapse? - avoided). Several secondary chains/clusters, with very larger craters up to ~ 2.8 km - fresh and degraded.

SFD Observations: 
Most of SFD dominated by class 4, but mid-sized craters also have a contribution from class 2 (tends to flatten SFD). Distribution < 1.5 km "steep", but shallower than other craters. Shallow "right ear" (more than 1 crater!, but only one point). Slope(Diff)=3.6 ± 0.4.

Discussion notes: 
floor is likely mare, plausible candidate for hard material and strength

Notes from Brian's adjustment:
- Counting boundary:
	Looks good.
	I disagree. There is material to the south east and west that looks different from the smooth material in the north east. I have decided to redefine boundary. (MRK)
	Some type 4 craters missed, but not many.

- Secondaries:
	Some clusters and chains were missed.

- Removal of large, buried craters:
	Looks OK.
	In the remaining area I think the large class 3 crater near the peak should be removed. It looks like it is filled with material that filled the north east section. (MRK)

- Size adjustment of large craters:
	Two largest craters should grow slightly.

- Explaining unusual cases:

- Future actions:

- Completed actions:
	Marked a few more type 4's (BLE).
	Fixed the size of the two large craters (BLE).
	Marked some more chains and clusters (BLE).
	Boundary redefined. (MRK)
	Added a few class 4 craters and changed some "primaries" to "secondaries". (MRK)

Last Edited by MRK 12/17/2012