A standard pattern syntax has been implemented for all HST instruments including NICMOS. During Cycles 7 and 7N, NICMOS patterns (dithering, chopping, mosaicing) were specified as an "Optional Parameter." Patterns are now implemented as a "Special Requirement" with different syntax. Previous Cycles 7 and 7N NICMOS Phase II pattern structures should not be followed when specifying patterns. There are a set of fifteen pre-designed patterns available for NICMOS observations. Users may define their own patterns as well, using the Pattern Parameters Form during Phase II development. The pre-defined patterns include four dithering patterns, four chopping patterns, five dither-chop patterns, and two mapping patterns.See Chapter 11 of the NICMOS Instrument Handbook for more details on chopping and dithering.
The following Phase II example includes the "Pattern_Data" for a four position dither pattern and the exposure line containing the pattern "Special Requirement". Note that parallels can be obtained at each pattern position, and that the pattern specification is only on the prime exposure.
Pattern_Number: 1 Primary_Pattern: Pattern_Type: NIC-SPIRAL-DITH Pattern_Purpose: DITHER Number_Of_Points: 4 Point_Spacing: 1.3 Coordinate_Frame: POS-TARG Pattern_Orient: 0 Center_Pattern: NO
Exposure_Number: 10 Target_Name: NGC6681 Config: NIC1 Opmode: MULTIACCUM Aperture: NIC1-FIX Sp_Element: F170M Wavelength: 1.70 Optional_Parameters: SAMP-SEQ=STEP8,NSAMP=9 Number_of_Iterations: 1 Time_Per_Exposure: DEF Special_Requirements: PAR 11,12 WITH 10 PATTERN 1 10-12 Comments: exp=31.963s
Exposure_Number: 11 Target_Name: ANY Config: NIC2 Opmode: MULTIACCUM Aperture: NIC2 Sp_Element: F160W Wavelength: 1.600 Optional_Parameters: SAMP-SEQ=STEP1,NSAMP=7 Number_of_Iterations: 1 Time_Per_Exposure: DEF Special_Requirements: Comments: exp=4.987s
Exposure_Number: 12 Target_Name: ANY Config: NIC2 Opmode: MULTIACCUM Aperture: NIC2 Sp_Element: F171M Wavelength: 1.71 Optional_Parameters: SAMP-SEQ=STEP8,NSAMP=8 Number_of_Iterations: 1 Time_Per_Exposure: DEF Special_Requirements: Comments: exp=23.969s