Thread: Regarding rotation of seismogram for right handed system

Sorry for the delay, but ...

If one simply flips the vertical, the header variable CMPINC will not be
correct
for that component.

CMPINC is defined as Component incident angle (degrees from upward
vertical)

To be complete one must change CMPINC for that component to 180 if one
multiplies it by -1.

While looking this up in the PDF manual, I found we had inadvertently left
out
the SAC Data File Format in the PDF manual (it is there in the HTML
version).
That will be fixed shortly.

Please let me know of any other problems in the PDF/HTML manuals.

Arthur



On 10/28/20 2:19 PM, sanjay Singh Negi (via IRIS) wrote:

Thank you for the correction.

Regards
Sanjay

On Wed, Oct 28, 2020, 22:53 Nabelek, John (via IRIS)
<sac-help-bounce<at>lists.ds.iris.edu <mailto:

sac-help-bounce<at>lists.ds.iris.edu>>

wrote:


Just multiply by -1.

On Oct 28, 2020, at 5:58 AM, Sanjay Singh Negi <sonoogeo<at>gmail.com

<sonoogeo<at>gmail.com>> wrote:

[This email originated from outside of OSU. Use caution with links

and

attachments.]

Hi John,
I never thought about it, but logically it seems correct.
It means that in order to flip, I need to rotate the vertical

component

to 180 degrees.

Thanks,
Sanjay


On Wed, Oct 28, 2020 at 1:31 AM Nabelek, John (via IRIS)

<sac-help-bounce<at>lists.ds.iris.edu
<sac-help-bounce<at>lists.ds.iris.edu>> wrote:

Sanjay

To convert right-handed system into left-haded, you will need to

flip

the vertical component.

For a high-handed system, positive vertical points down.

-John

On Oct 27, 2020, at 5:11 AM, Geo . (via IRIS)

<sac-help-bounce<at>lists.ds.iris.edu
<sac-help-bounce<at>lists.ds.iris.edu>> wrote:

[This email originated from outside of OSU. Use caution with

links and

attachments.]

Hello Sanjay,
Based on the SAC documentation, your description of components,

and

assuming that your

orientation correction is clockwise from north (+80?, how did you

estimate this?), it seems that "rotate to -80 reverse" is correct.

"Reverse" indicates that H2 is pointing north and H1 is pointing

east:

the second component is lagging the first by 90°. Think of it as the
reverse convention as, usually, H1 and H2 are pointing north and east
respectively.

http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html

http://www.adc1.iris.edu/files/sac-manual/commands/rotate.html

Januka

On Tuesday, 27 October 2020, sanjay Singh Negi (via IRIS)

<sac-help-bounce<at>lists.ds.iris.edu
<sac-help-bounce<at>lists.ds.iris.edu>> wrote:

Hi Sac users,
I have OBS record that follows the

right-handed

system in which H2 component is 90 degree counter-clockwise of H1.

Horizontal component data file are as following:
2018.128.01.00.45.420.X.sac ---> East component
2018.128.01.00.45.420.Y.sac ----> North component
2018.128.01.00.45.420.Z.sac ----> Vertical component

The orientation correction angle is 80 degree.

For rotation, I use the following scheme:
sac>> read 2018.128.01.00.45.420.Y.sac

2018.128.01.00.45.420.X.sac

sac>> rotate to 80 reverse


Could you please comment on whether the command I give is

correct or not?

Why I am confused about rotation is because of two following

reasons:

1: To get true north-south rotation for an OBS record the

orientation

correction of 80 degrees has to be made. For this, logically

-80/360-80

degree should be implemented to rotate it back to North-South. Would

+80

degree be fine?

2. What exactly sac does on applying reverse at the end of

rotate command?

Thanks in advance.

Regards
Sanjay

----------------------
SAC Help
Topic home: http://ds.iris.edu/message-center/topic/sac-help/ |
Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu

Sent from the IRIS Message Center (http://ds.iris.edu/message-center/)
Update subscription preferences at http://ds.iris.edu/account/profile/