Analysis of Seeing in the Surface Layer at Paranal

J. Navarrete (ESO), March 2008

 

1-   Seeing Above Surface Layer (ASL)

The ASL seeing correlates well to VLT-UT science image quality (messenger-no132-11, June 08). The ASL seeing is computed from contemporaneous DIMM-MASS_LITE data (Sep.2004 to July 2007) as in E-ELT-TRE-222-0215.pdf:

 

Seeing(ASL) = (0.22 * DIMM5/3 + 0.78 * MASS5/3)3/5

 

 

 

Min

5perc.

Median

Average

95perc.

Max

Std. dev

Samples

DIMM Seeing (arcsec)

0.26

0.52

0.86

0.96

1.77

5.86

0.42

177904

ASL Seeing (arcsec)

0.18

0.32

0.57

0.64

1.18

3.46

0.28

177904

UT1 S-H CASS corr. seeing (arcsec)

0.28

0.40

0.63

0.67

1.04

1.89

0.19

23888


2-ASL seeing as function of the Wind at 30mts (>2m/s)

 

Case 1: ASL seeing <= 0.5 (55940 samples)

 

 

Case 2: 0.5 < ASL seeing <= 1.0(87351 samples)

 

 

Case 3: ASL seeing > 1.0(17124 samples)

 

3-   Seeing Below Surface Layer (BSL) as function of the Wind at 30mts (>2m/s)

BSL seeing = 0.78 * (DIMM5/3 MASS5/3)3/5

 

Case 1: BSL seeing <= 0.5 (85104 samples)

 

 

Case 2: 0.5 < BSL seeing <= 1.0(62764 samples)

 


Case 3: BSL seeing > 1.0(12547 samples)

 

 

 

Monthly BSL average seeing as function of the Wind Direction for bad seeing

 


Appendix:    Microthermal measurements in 1998

An earlier study based on microthermal sensor measurements had concluded to a much smaller chare of the first 30m in the total seeing:

Measurement of the microthermal activity and Seeing at Paranal (GSM Campaign, Nice University) during a night presenting variable conditions.


The contribution of the layer 2-21m above ground corresponds to an increase of about 8% of the seeing.


Publication

00b
F. Martin, R. Conan, A. Tokovinin, A. Ziad, H. Trinquet, J. Borgnino, A. Agabi and M. Sarazin; Optical parameter relevant for high angular resolution at Paranal from GSM instrument and surface layer contribution; Astron. Astrophys. Supplement, v.144, p.39-44; June 2000 (pdf).