Level 1.5 Geolocation

Martin Bates, RAL

GIST 24

15th December, 2005

Questions

• How good is the level 1.5 GEO ?– is it an option for release ?– what known problems are there ?

• How would we handle operationally N/S & E/W drifts in a release ?

• What, if necessary, could be done on a short time scale to produce an improved GEO ?

• What are the longer term prospects for fixing the level 1.5 GEO ?

How good ?

elevation off-centre

azimuth (vs col) elevation (vs row)

Known Problems

• Derivation of a “good” optical model

• Axis misalignments– spin axis study – N/S drifts

• East-west systematic jump with change in rotation rate

• Noise in SOL_SOE_Delay

Derivation of a Good Optical Model

Observed rotation of banana in RGP L15G 90 min fits

N/S Shift

N/S Shift commencing 15 Jan 2005

Manually Tracking N/S Changes

• Changes since 04 Nov• 0.05 pixel: 12 changes• 0.l pixel: 5 changes• 0.2 pixel: 1 change

Tracking N/S Shifts

Start Time End Time N/S Tuning Param2 Param3

20051207 00:00:00 21000101 00:00:00 -0.0245 0 0

20051204 00:00:00 20051207 00:00:00 -0.021 0 0

20051202 00:00:00 20051204 00:00:00 -0.0175 0 0

20051129 00:00:00 20051201 00:00:00 -0.014 0 0

20051127 00:00:00 20051129 00:00:00 -0.0105 0 0

20051124 00:00:00 20051127 00:00:00 -0.007 0 0

20051121 00:00:00 20051124 00:00:00 -0.0035 0 0

20051111 00:00:00 20051121 00:00:00 0 0 0

20051110 00:00:00 20051111 00:00:00 -0.0035 0 0

20051109 00:00:00 20051110 00:00:00 -0.007 0 0

20051107 00:00:00 20051109 00:00:00 -0.014 0 0

20051105 00:00:00 20051107 00:00:00 -0.0105 0 0

20051104 00:00:00 20051105 00:00:00 -0.007 0 0

19990101 00:00:00 20051104 00:00:00 0 0 0

New data table – quickly tune N/S GEO

Automatic Tracking of N/S Changes• Use difference between

image and GEO– needs GEO to have run in

order to run the GEO

– 2 pass process

• However, relatively slowly varying, so could use results from one image to process next– could use running average (as with gains but smaller τ)

– enforce strict time order to processing (SDPL0 change)

– handle systematics (espec. stray light)

• Would take significant development time to implement.

Spin Axis Correction

• IMPF makes a correction to spin axis as supplied by flight dynamics (SEV header)

• Have sample data (24 hrs) for 04 May, 16, 17 Aug, 28, 29 Oct: Δx, Δy, Δz over 24 hours

• What does it mean ?– a.) simple spin correction, no misalignment:

• r_spin = r_orig + r_corr

– b) gives spin axis to structural axis misalignment• need to know frame of reference to work out how to use it

• Further investigations at EUMETSAT.• Processing tests for moment assume a.)

Spin Axis Test : Aug vs Oct 05

Aug 17

Oct 29

Normal Proc. Spin Axis Corr.

Can spin axis correction account for 0.75 pixel jump in N/S geolocation ?

No 2 pixel jump

Regular spin axis correction ?

• As part of change to include TSOL jitter, and switch to transfer of L0 data by sftp:– asked for ~ 100 bytes of blank data in packet for spin axis

correction et al.– too late for negotiations between EUMETSAT and contractor– means that any future change request will also involve UMARF

(pkt size increase)– messy TSOL jitter style solution for spin axis corr ?

• could be more slowly varying

• Data only seem to have been recorded since 03 Feb 2005– but suggests looking at horizon, landmark and star position info in

SEVIRI trailer– may be able to regenerate error curves– would be regenerated by a SEVIRI reprocessing

Spin-Structure MisalignmentzSATspin axis

z

x

spin axis correction

Incomplete knowledge of E/W centring shifts with spin rate

Spin rate change associated with 08 Feb manoeuvre No rotation rate change

Retuning

Questions

• How good is the level 1.5 GEO ?– is it an option for release ? See later talks.– what known problems are there ?

• optical model, N/S drifts, lack of knowledge of misalignments...• How would we handle operationally N/S & E/W drifts in a release ?

– N/S: improved monitoring for spotting drifts quickly– N/S: new parameter and data table to implement tunings quickly– E/W: advance notice of spin rate changes; more stable (TSOL Jitter).

• What, if necessary, could be done on a short time scale to produce an improved GEO ?– improved optical model ? (see later talks)– automated system for N/S tunings ?

• What are the longer term prospects for fixing the level 1.5 GEO ?– improved optical model– better understanding of spin axis correction– access to MSG spin-structure misalignment– model for E/W centring with rotation rate– study use of FIFO data in conjunction with SOL_SOE.