Data were obtained for the purpose of measuring the relative throughput of the Near-IR Science Instruments (SIs) of the James Webb Space Telescope (JWST) as part of the second and third cryogenic-vacuum tests (CV2CV3) of the Integrated Science Instrument Module (ISIM) conducted at the Goddard Space Flight Center (GSFC) in 2014 and 20152016, at the beginning and end of the environmental test program, respectively. This Poster focuses on data obtained as part of the Initial Optical Baseline and as part of the Final Performance test -- two epochs that roughly bracket the CV3 test. The purpose of the test is to trend relative throughput to monitor for any potential changes from gross problems such as contamination or degradation of an optical element. Point source data were taken at a variety of wavelengths for NIRCam Module A and Module B, NIRSpec, NIRISS, Guider 1 and Guider 2 using the Laser Diode (LD) 1.06 micron, LD 1.55 micron, 2.1 micron LED and 3.5 micron LED, as well as for NIRCam Mod A and B and NIRISS using a tungsten source and the F277W, and F480M filters. Spectra were taken using the G140M, G235M, and G395M gratings for NIRSpec, the GRISMR grism for NIRCam Mod A and B and the GR150C grism for NIRISS. The results of these measurements are compared to what would be expected given the efficiency of each of the optical elements in each SI. Although these data were taken as a check against gross problems, they can also be used to provide the first relative throughput estimate for each SI through the various filters source wavelengths measured in their flight-like configurations

Birkmann, Stephan

Kelly, Douglas M.

Kimble, Randy A.

Lindler, Don

Malumuth, Eliot

Martel, Andre

Ohl, Raymond G.

Rieke, Marcia J.

Rowlands, Neil

Te Plate, Maurice

NASA Technical Reports Server

) CV3 Data Collection 
	
•  The	knowledge	of	detector	gains	are	most	likely	the	largest	source	of	error	in	the	ra6o	of	the	throughput	of	one	SI	to	another.		We	
es6mates	the	error	in	the	gain	to	be	about	2%	for	NIRSpec	and	5%	for	all	other	SI	detectors.	However	this	cancels	when	comparing	
results	form	the	Ini6al	Op6cal	Baseline	to	the	Final	Performance	(unless	the	gain	has	changed	between	them).	
•  Photon	noise	-	The	Shot	noise	associated	with	the	measurements	of	the	detected	number	of	DN	within	the	selected	aperture	is	a	
source	of	random	error	in	each	SI	throughput	and	thus	in	the	ra6o.		
•  Determining	the	background	to	subtract	has	an	inherent	uncertainty.	We	es6mate	this	from	the	growth	curve	for	the	point	source	
data	(as	described	above)	and	from	the	background	extrac6ons	for	the	spectral	data	(as	described	above).	
•  A	linearity	correc6on	may	be	needed	–	Although	an	eﬀort	was	made	in	collec6ng	the	data	to	avoid	going	into	the	most	non-linear	
regime	this	was	not	always	the	case,	especially	for	the	Ini6al	Op6cal	Baseline	LED35	data.	
•  Source	Stability	–	Data	taken	for	one	SI	at	the	start	and	end	of	each	sequence	shows	that	with	the	excep6on	of	the	Ini6al	Op6cal	
Baseline	LED35	data	the	diﬀerence	was	always	less	than	4%	and	usually	less	than	2%	(the	Ini6al	Baseline	LED35	diﬀerence	was	
7.5%).	
•  The	eﬀect	of	the	pupil	oﬀset	–	The	Code	V*	model	computed	correc6ons	for	the	percent	clipped	amounted	to	less	than	2%	in	all	
cases.		Any	error	is	therefore	the	error	in	compu6ng	the	correc6on	–	a	frac6on	of	a	small	percentage.	
•  The	model	images	may	not	match	the	actual	PSF	–	This	would	produce	an	error	in	the	derived	aperture	correc6ons	–	(Probably	a	
small	error).	
•  The	input	spectra	may	not	be	known	well	enough	–	Producing	an	error	in	the	correc6on	for	source	clipping	by	the	ﬁlters.	This	is	
especially	be	a	problem	for	LED35	(see	the	next	panel)	
•  The	quantum	yield	correc6on	for	lower	wavelengths	may	be	diﬀerent	from	what	we	used.	–	1.25	for	1.06	µm	and	1.085	for	1.55	
µm.	
•  The primary purpose of this test was to trend the relative throughput 
of the JWST near-IR science instruments (NIRCam, NIRSpec, 
NIRISS, and FGS) as a way to monitor for any potential changes 
from gross problems such as contamination or degradation of an 
optic.   
•  These results also give the first relative throughput of the 
instruments in their flight-like configurations and can be used to 
verify and update model predictions. 
•  They can also be used for trending with the on-orbit throughputs that 
will be measured during commissioning. 
•  Data was obtained during Cryo-Vacuum testing of the Integrated 
Science Instrument Module (ISIM) at the Goddard Space Flight 
Center (GSFC) as part of 2 test procedures, the Initial Optical 
Baseline (IOB) December 29, 2015 and the Final Performance (FP) 
January 25, 2016 (which bracket most of the SI testing in this Cryo-
Vacuum test).  The results will also be compared to a similar test 
from a previous Cryo-Vacuum test (data from September 14, 2014) 
to bracket ISIM-level testing. 
Purpose of Test 
Eliot	Malumuth2,	Stephan	Birkmann3,	Douglas	M.	Kelly4,	Randy	A.	Kimble1,	Don	Lindler5,	André	Martel6,	Raymond	G.	Ohl1,		
Marcia	J.	Rieke4,	Neil	Rowlands7,	Maurice	Te	Plate8	
	
1NASA's	GSFC,	2Wyle	STE/NASA's	GSFC,	3European	Space	Agency/STScI,	4Steward	Observatory,	University	of	Arizona,	5Sigma	Space	
CorporaKon/NASA's	GSFC,	6STScI/NRC	Herzberg,	7Honeywell	Aerospace,	8European	Space	Agency	
	
Source NRCA3 NRCB4 NRCALONG NRCBLONG NIRISS NRS1 FGS1 FGS2 
LD106 1800 1800 1800 1800 1800 1800 
LD155 2200 2200 2200 2200 2200 2200 
LED21 30000 30000 30000 30000 30000 30000 
Tungsten/F277W 400 @ 
T=1200 
400 @ 
T=1200 
400 @ 
T=1200 
LED35 4500 
2600 
4500 
2600 
4500 
2600 
4500 
2600 
4500 
2600 
4500 
2600 
Tungsten/F480M 4000 @ 
T=1200 
4000 @ 
T=1200 
4000 @ 
T=1200 
Point Source Observations 
Flux setting and temperature for each source is shown.  NIRISS exposures were 
1.1 to 1.9% clipped and NIRSpec exposures were 0.3 to 0.5% clipped by having to 
move the Pupil Select Mechanism to reach the fiber to those instruments, all others 
were 0.2% clipped or less.   
 
The same source and flux setting was used for each Science Instrument for a direct 
comparison at 1.06, 1.55, 2.1, and 3.5 µm for all Science Instruments, and at 2.77 
and 4.8 µm for NIRCam LW and NIRISS.  The source was shuttered but not turned 
off between exposures for the different instruments. 
Data Collection (IOB & FP) 
Spectral Observations 
Science Instrument 
GRISM/GRATING 
F277W F322W2 F444W F150W F200W F150LP F170LP F290LP 
NIRCam Mod A 
GRISMR 
900 @ 
T=1200 
900 @  
T=1200 
900 @  
T=1200 
NIRCam Mod B 
GRISMR 
900 @  
T=1200 
900 @  
T=1200 
900 @  
T=1200 
NIRISS 
GR150C 
900 @  
T=1200 
900 @  
T=1200 
NIRSpec  
GR140M 
900 @  
T=1200 
NIRSpec  
GR235M 
 
900 @  
T=1200 
 
NIRSpec  
GR395M 
 
900 @  
T=1200 
 
A flux setting of 900 and temperature setting of 1200 was used for the tungsten 
source..  NIRISS exposures were ~1.1% clipped and NIRSpec exposures were 
~0.6% clipped.   
 
The source and source flux setting was the same for all instruments spectral 
exposures.  The source was shuttered but not turned off between exposures for the 
different instruments. 
   
Conclusions 
1.  	BoPom	Line:	RelaRve	NIR	SI	throughputs	look	good	–	This	test	was	conceived	as	
a	check	to	make	sure	that	none	of	the	Near-IR	Science	Instruments	has	a	gross	
problem	(e.g.	contamina6on,	degrada6on	of	an	op6c).		All	comparisons	show	
rela6ve	throughput	reasonably	close	to	expecta6ons	(with	the	largest	uncertainty	
for	the	LED35	3.5µm	comparison	–	the	shape	of	the	LED	spectrum	appears	to	
change	with	ﬂux	in	a	way	that	explains	the	larger	uncertainty	for	the	LED35	data).	
	
2.  	PredicRons	of	throughput	(using	an	opRcal	component	model)	are	in	
reasonable	agreement	with	what	we	observe	–	This	shows	that	the	measured	
component	curves	are	a	fairly	good	representa6on	of	the	actual	response	of	each	
element	with	wavelength.	
	
3. 	The	SensiRvity	Requirement	for	the	ISIM	–	There	is	a	requirement	that	the	
Science	Instruments	for	James	Webb	Space	Telescope	(JWST)	reach	certain	
sensi6vity	performance	levels.		These	requirements	are	veriﬁed	by	a	combina6on	
of	instrument	tes6ng	and	analysis	of	the	component	eﬃciencies.	The	results	of	the	
throughput	cross	calibra6on	test	show	that	the	component	eﬃciency	curves	as	
measured	in	the	past	are	close	to	what	is	in	the	delivered	science	instruments.		The	
results	of	this	test	serves	as	a	cross	check	that	the	ISIM	module	meets	the	
sensi6vity	requirements.	
1.  Calibrated data (a slope fit the non-destructive read “up the ramp”) was used for this analysis. Note, while 
these reductions subtract a dark image and divide by a flat field no linearity correction is applied.  
 
2.  The	calibrated	image	is	read	in	as	is	the	data	quality	image.		Pixels	ﬂagged	as	hot	pixels	in	the	data	quality	image	are	
replaced	by	the	average	of	the	neighboring	pixels	in	the	image.	Visual	inspec6on,	and	planned	poin6ng	loca6on	
selec6on,	showed	that	no	hot	pixels	were	inside	the	core	of	the	PSF	(where	interpola6on	would	not	be	accurate).	
	
3.  A	background	exposure	treated	in	the	same	way	is	subtracted	where	applicable	(FGS	exposures,	NIRSpec	exposures	
using	the	Long	Pass	ﬁlters,	the	LED35	and	F480M	exposures	all	SIs).	
	
4.  A	column	average	of	~200	columns	was	taken	on	either	side	of	the	point	source	(several	hundred	pixels	away)	and	
then	averaged	and	subtracted	column	by	column	in	the	data	image	to	remove	row	by	row	diﬀerences	in	the	bias.	
	
5.  Photometry	was	done	using	a	Growth	Curve	(counts		
						within	concentric	circular	apertures	centered	on	the		
						Gaussian	peak	of	the	PSF.		Background	was	measured		
						from	radius	22	–	30	pixels	(typically)	but	was	smaller		
						for	NIRSpec	because	of	the	small	size	of	the	Imaging		
						window	(7-10	pixels).	
	
6.  A	total	number	of	DN	was	then	selected	within	a	radius		
						of	15	pixels	(NIRCam	SW),	10	pixels	(NIRCam	LW,	NIRISS,	
						and	FGS),	and	5	pixels	(NIRSpec).	
	
7.  DN	changed	to	e-/sec	-	mul6ply	by	the	gain	and	divide	by	exposure	6me.		The	gains	used	were	derived	using	data	from	
the	NIRCam,	NIRISS,	and	FGS	linearity	tests.	NIRSpec	gain	was	derived	from	detector	tes6ng	done	at	GFSC.		Note:	the	
uncertainty	in	the	gain	is	the	largest	error	in	the	ra6o	of	the	throughput	of	one	SI	to	another.		
	
8.  Apply	Aperture	correc6on	–	Aperture	correc6ons	were	derived	using	model	images	which	take	into	account	the	source	
spectrum	and	all	of	the	op6cal	elements	of	the	science	instrument.		These	noiseless,	zero	background	model	images	
were	treated	in	the	same	as	the	data	images.		The	ﬂux	within	the	same	aperture	as	was	used	with	the	data	was	
compared	to	the	total	and	a	correc6on	was	derived.	Typically	the	correc6ons	were	~5%	for	the	bluer	bands	and	
~10-15%	for	the	redder	bands.	
9.  Apply	correc6on	for	clipping	due	to	oﬀ	nominal	pupil	–	Correc6ons	done	using	Code	V*	models.	
10. Apply	correc6on	for	quantum	yield	eﬀect	for	LD106	and	LD155	data	–	Correc6on	using	the	wavelength	cut	oﬀ	gives	
~25%	for	all	detectors	at	1.06	microns	and	~8.5%	at	1.55	microns	except	for	NIRCam	SW	(where	the	2.5	µm	cutoﬀ	
leads	to	no	correc6on).		
11. Apply	correc6on	for	diﬀerent	band	pass	–	Although	the	source	is	the	same,	the	light	passes	through	diﬀerent	ﬁlters	(or	
in	the	case	of	FGS	no	ﬁlter)	for	diﬀerent	Science	Instruments.		-	The	integral	of	the	source	spectrum	across	a	ﬂat	
topped	normalized	to	1.0	ﬁlter	curve.	
*Synopsys	Corp.,	Mountain	View,	CA	
Red squares are raw counts. 
 
Blue diamonds are after a background value 
has been subtracted 
1.  NIRSpec	data	was	reduced	to	DN/sec/micron	by	Stephan	Birkmann	of	the	NIRSpec	team.	
2.  NIRCam	and	NIRISS	data	were	reduced	using	the	calibrated	data	and	treated	the	same	way	as	the	point	source	data.	
	
3.  One	dimensional	spectra	were	extracted		
						from	the	spectral	images	using	a	wide	slit		
						to	make	sure	we	got	virtually	all	of	the	ﬂux		
						from	the	source.		Background	was	measured	
						in	slits	of	the	same	size	above	and	below	the		
						spectra,	averaged	and	subtracted.	
	
4.  Wavelength	Calibra6on	for	NIRCam	and		
							NIRISS	–	The	ﬁlter	curve	long	and	short	wave		
							cutoﬀ	give	the	wavelength	scale	in	combina6on		
							with	the	dispersions	measured	by	the	NIRCam		
							and	NIRISS	teams.	
5.  The	spectra	were	divided	by	the	exposure	6me		
						and	the	dispersion	and	mul6plied	by	the	gain	to		
						put	the	units	into	e-/sec/µm.	
	
	
	
	
	
	
NIRISS F200W 
1	
Results	–	Throughput	rela6ve	to	NIRCam	Mod	A	
•  Blue = Initial Optical Baseline (Dec 29, 2015),, Green = Final Performance (Jan 25, 2016), Red = data from Sept 
14, 2014 (note the detectors were changed after these data were collected), , Orange = Model Predictions. 
•   Blue vs. Green is a measure of stability across the recent Cryo-Vac test. 
•  Green vs. Orange is a measure of the accuracy of the instrument component efficiencies. 
 
               Comparison of relative Throughput to expected from the SI components relative Throughput 
Source NRCA3 NRCB4 NRCALONG NRCBLONG NIRISS NRS1 FGS1 FGS2 
LD106 1.000 
1.000 
1.049 
1.024 
1.189 
1.132 
1.055 
1.031 
1.051 
1.007 
1.047 
1.010 
LD155 1.000 
1.000 
1.022 
0.987 
1.065 
1.029 
1.014 
0.984 
0.821 
0.896 
1.104 
1.076 
LED21 1.000 
1.000 
0.982 
0.948 
0.851 
0.830 
1.069 
1.028 
0.838 
0.914 
1.000 
0.939 
Tungsten/F277W 1.000 
1.000 
1.038 
1.012 
0.997 
0.974 
LED35 1.000   
1.000 
0.986 
0.977 
0.901 
0.890 
1.202 
1.256 
1.035 
1.253 
1.184 
1.280 
Tungsten/F480M 1.000   
1.000 
0.980 
0.961 
0.782 
0.851 
Each number represents the ratio          measured (SI/NIRCam A) 
  Model (SI/NIRCam A)  
 
The numbers in blue are from the Initial Optical Baseline  
The numbers in green are from the Final Performance 
Results	–	Spectral	Comparison	
The NIRSpec Spectra divided by the NIRISS Spectra (top) and by the NIRCam module A (red curve) and module 
B (green curve) Spectra (bottom) for the FP data.  Higher numbers are lower throughput relative to NIRSpec.  
Note how NIRCam B has lower throughput than NIRCam A. 
 	
The	point	source	exposures	of	the	LED35	source	have	the	largest	diﬀerences	with	the	
predicted	ra6o	to	NIRCam	module	A.		This	is	especially	true	for	NIRSpec	(using	a	long	pass	
ﬁlter)	and	Guider	1	and	2	(no	ﬁlter)	and	especially	in	the	Final	Performance.		Spectra	of	
the	LED35	source	taken	with	the	NIRSpec	prism	on	August	7,	2014	and	the	G395M	
gra6ng	on	December	29,	2015	show	that	there	is	a	long	red	tail	that	is	outside	the	ﬁlter	
bandpass	for	NIRCam	and	NIRISS.		The	power	in	this	tail	may	be	a	func6on	of	the	ﬂux	
seing.			
1	
The blue curve is the prism spectra spectra of the LED35 source taken August 7, 2014 
The red curve is the G395M spectra of the LED35 source taken December 29, 2015. 
 
 
2.5 3.0 3.5 4.0 4.5 5.0
Wavelength (microns)
0.0
0.2
0.4
0.6
0.8
1.0
N o
r m
a l
i z e
d  
F l
u x
N o
r m
a l
i z e
d  
F l
u x
Dec 29, 2015 Spectra flux was      130,000  
August 7, 2014 Spectra flux was     80,000 
Initial Optical Baseline flux was         4,500  
Final Performance flux was               2,600 
The difference in the red tail may be an indication that the tail is more pronounced with a lower flux 
setting in keeping with the larger than expected ratio of observed Guider and NIRSpec to NIRCam A 
throughput during the Final Performance relative to the Initial Optical Baseline. 
 
NIRCam	B					NIRSpec									NIRISS									Guider	1						Guider	2	
2.5	
	
2.3	
	
2.1	
	
1.9	
	
1.7	
	
1.5	
	
1.3	
	
1.1	
	
0.9	
	
0.7	
	
0.5	
	
	
	
Re
la
6v
e	
to
	N
IR
Ca
m
	M
od
	A
	
	 	 	
NIRCam	B					NIRSpec									NIRISS									Guider	1						Guider	2	
Re
la
6v
e	
to
	N
IR
Ca
m
	M
od
	A
	
	 	 	
1.7	
	
	
1.5	
	
	
1.3	
	
	
1.1	
	
	
	
0.9	
	
	
0.7	
	
	
0.5	
	
	
	
NIRCam	B					NIRSpec									NIRISS									Guider	1						Guider	2	
Re
la
6v
e	
to
	N
IR
Ca
m
	M
od
	A
	
	 	 	
1.7	
	
	
1.5	
	
	
1.3	
	
	
1.1	
	
	
	
0.9	
	
	
0.7	
	
	
0.5	
	
	
	
NIRCam	B																												NIRISS	
1.3	
	
1.2	
	
1.1	
	
1.0	
	
	
0.9	
	
0.8	
	
0.7	
	
0.6	
	
0.5	
	
	
	
Re
la
6v
e	
to
	N
IR
Ca
m
	M
od
	A
	
	 	 	
NIRCam	B					NIRSpec									NIRISS									Guider	1						Guider	2	
Re
la
6v
e	
to
	N
IR
Ca
m
	M
od
	A
	
	 	 	
2.5	
	
2.3	
	
2.1	
	
1.9	
	
1.7	
	
1.5	
	
1.3	
	
1.1	
	
0.9	
	
0.7	
	
0.5	
	
	
	
NIRCam	B																												NIRISS	
Re
la
6v
e	
to
	N
IR
Ca
m
	M
od
	A
	
	 	 	
2.1	
	
1.9	
	
1.7	
	
1.5	
	
1.3	
	
1.1	
	
0.9	
	
0.7	
	
0.5	
	
	
	
The Blue curve is the combined NIRSpec  
G140M, G235M and G395M spectrum. 
 
The Red curve is the combined NIRCam Module A  
GRISMR F277W, F322W2, and F444W spectrum.  
 
The Green curve is the combined NIRCam Module B  
GRISMR F277W, F322W2, and F444W spectrum.  
 
The Gold curve is the combined NIRISS 
 F150W and F200W spectrum   
Fl
ux
		e
- /s
ec
/µ
m
)	
					1																																									2																																										3																																									4																																									5	
Wavelength	(µm)	
N
IR
S
pe
c/
N
IR
C
am
 
N
IR
S
pe
c/
N
IR
IS
S
 
Wavelength	(µm)	
2.5																										3.0																												3.5																											4.0																												4.5																											5.0	
																				1.4																												1.6																											1.8																												2.0																												2.2	
NIRSpec	G140M	&	G235M	vs.	NIRISS	GR150C	
NIRSpec	G235M	&	G395M	vs.	NIRCam	A	&	B	GRISMR	
https://ntrs.nasa.gov/search.jsp?R=20160006642 2019-08-31T02:39:48+00:00Z


Relative Throughput of the Near-IR Science Instruments for the James Webb Space Telescope as Measured During Ground Testing the Integrated Science Instrument Module

Relative Throughput of the Near-IR Science Instruments for the James Webb Space Telescope as Measured During Ground Testing the Integrated Science Instrument Module

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