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Landsat 9 Thermal Infrared Sensor 2 Preliminary Stray Light Assessment

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Landsat 9 Thermal Infrared Sensor 2 Preliminary Stray Light Assessment TIRS-2 Instrument Project Thermal Infrared Sensor-2 Landsat 9 Thermal Infrared Sensor 2 Preliminary Stray Light Assessment Joel McCorkel (NASA Goddard) Matt Montanaro (NASA Goddard) June Tveekrem (NASA Goddard) John Stauder (Space Dynamics Lab) Allen Lunsford (NASA Goddard) Eric Mentzell (NASA Goddard) Jason Hair (NASA Goddard) Dennis Reuter (NASA Goddard) 1 Stray Light Assessment Objective for TIRS-2 • Landsat 8 / Thermal Infrared Sensor – 1 (TIRS-1) has significant stray light in its optical system. • Landsat 9 / TIRS-2 is a near-replica of TIRS-1. • Stray light effects on TIRS-1 imagery have now been corrected in the ground processing system. • To prevent the problem with TIRS-2, the instrument has built-in mitigations to drastically reduce stray light. • Major effort to model and test the design changes in TIRS-2. • Results of the initial scattering measurements in thermo-vacuum conditions along with results of the optical scattering model are presented here. 2 Stray Light Problem on Landsat 8 / TIRS-1 • Landsat 8 / TIRS-1 instrument found to have a stray light issue where off-axis radiance scatters onto the focal plane. • Demonstrated through on-orbit out-of-field scans of the Moon. Moon position 15-deg Field-of-View & approx. size Detector A Detector B k-- bandlO ~ bandll Detector C Scattered Signal 3 Lunar Scans for TIRS-1 • Flagged lunar locations where scatter was recorded by the detectors. • Discovered that there 40 is a strong scattering 30 source in the optical system approximately 20 13-deg off-axis. 10 , 0)Q) I 0. • Very weak 22-deg "a;" o· Ol C: scatter also observed <:I'.: (not indicated here) Strong -30 13-deg scatter -40 Band 10 Band 11 -50 ~-~-~-~-~ -50 ~-~-~-~-~ -20 -10 0 10 20 -20 -10 0 10 20 Angle [D eg] Ang le [Deg] 4 Cause of Scattering for TIRS-1 • Detailed optical models pin-pointed scattering surface in the telescope. Strong scatter Weak scatter TIRS-1 Optical Telescope System source (13-deg) source (22-deg) Focal Plane Lens 1 Lens 2 Lens 3 Lens 4 5 Solution to Scattering for TIRS-2 • Baffles added to TIRS-2 design to cut off scattering paths. TIRS-2 Optical Telescope System Baffles Added Baffles Added Focal Plane Lens 1 Lens 2 Lens 3 Lens 4 6 TIRS-2 Optical Model & Lab Measurements • Laboratory measurements confirmed optical design change. 1.0E+OO --T,est data, no baffles M,odel, no lbaiffl,es 1.0E-01 - T,est data, w'th ba·ffles. ---- M,odel, witll, bafflles 1.0 -iO:Z 1.0 -IQ 1.0 .04 ... 1.0E-05 1.0E-06 13-deg Scatter 22-deg Scatter 1.0 -i07 8 10 12. 1.4 16 18 2.0 22 24, 26 28 30 ln,cidlent Angle (deg) 7 TIRS-2 TVAC Measurements • Thermal-vacuum (TVAC) testing required for “flight-like” verification since TIRS-2 is a cryogenic instrument (190 K optics; 40 K focal plane). • Initial TVAC known as TIRS-2 Imaging Performance and Cryoshell Evalution (TIPCE) consists of flight telescope, focal plane, electronics. • Calibration ground support TVAC Chamber Overview equipment (CGSE) provides a variable-aperture blackbody source that can be “steered” around the field of view of the instrument. TIRS-2 • For this TVAC test, able to telescope/ scan the source -28 deg to focal +18 deg in azimuth and -8 plane deg to +12 deg in elevation CGSE Blackbody CGSE Steering & Collimator Mirror 8 TIRS-2 TVAC Scattering Data Single image frame corresponding Diagram of source location to the source location % relative to detectors B 0.03 ,......, ,/,,., A 0) -10 22I ° 13° (l) ... .{ .... Band 10 "C ::1::::: 0.025 L.......J : ~.: :: :: .... * -5 C ;i::::::•t••···· i :,t:: 0 .le•••••• A Band 11 :+=, .. ;r== 0.02 ro 0 t ...... ::j; :: • > ... ..... (l) ·i...... .J~ .. C 0.015 w 5 : :r!: :: :: :::::{: ::!,::::: ::::::: ~ :·••t••·· :: ~'i: :: Cl) 10 .. .. ::::.{,:: 0.01 -30 -20 -10 0 0.005 SM Azi uth [deg] C 0 r Blackbody source is here Units are percent of the signal when the target is directly No scatter recorded on detectors illuminated on the detectors 9 TIRS-2 TVAC Scattering Data @ 13 deg Single image frame corresponding Diagram of source location to the source location % relative to detectors B 0.03 ,......., / A 0) -10 22I ° 13° (l) ... /..... / Band 10 ;:Q, ::z::::: :: : ;l. 0.025 -5 : ~-: :: :: ::i: C: :t:::::: •,:: Band 11 0 ·1t ..... ~ : :: A :.p , ... 0.02 co 0 r::::: ;::: ,~ • > ........ ... (l) :i:::::: :.r C 0.015 w 5 :); : :::: ........ 0.03% ::!,::::: ..;;m ·~· ~ : :: 1:: :: (./) 10 .. .. ......... x .. ...... 0.01 -30 -20 -10 0 0.005 SM Azi uth [deg] C 0 r Blackbody source is here (13 deg) Units are percent of the signal when the target is directly Scatter recorded on detectors illuminated on the detectors 10 TIRS-2 TVAC Scattering Data @ 22 deg Single image frame corresponding Diagram of source location to the source location % relative to detectors 0.03 ,......, A B 0> -10 22I ° 13° (l) ...... .{ .... Band 10 "C :: :::1::::: 0.025 L......J -5 :: C :: ~:: :: :: 0 :: ~:::::: A Band 11 :: :: I::::::: 0.02 ~ 0 ..•• .•••••••• ...... > ............. ... ..... (l) •• • • ~· •• • • • •• •• •••••• C 0.01% 0.015 w 5 ............ .. ,. ..... ::•••• :: !•t••··,::::: :: ::,:~\::: ..... ~ 10 .. :: :::·:.{,:: 0.01 -30 - 0 -10 0 0.005 SM imuth [deg] C 0 r Blackbody source is here (22 deg) Units are percent of the signal when the target is directly Scatter recorded on detectors illuminated on the detectors 11 TIRS-2 Measured Scattering Sources • Similar to TIRS-1 lunar scans, flag out-of-field source locations with the magnitude of the scattering signal at that location (band 11 shown here) 0.03 -20 Each pixel represents the scatter magnitude of the out-of-field -115 source location 0.025 -110 /~ ......., 0.02 C) \ (]) -5 1J L......J A B C 0 0 :+=i 0.015 [%] ct:l > C (]) w 5 TIRS-2: 0.03%0.01 10 (TIRS-1: 0.4%) ~ e9 15 TIRS-2: 0.01% 0.005 Total area(TIRS scanned-1: 0.024%) / 20 in TVAC _#/ 0.00 -20 -10 0 10 20 Azimuth [deg] 12 TIRS-2 Scattering Sources vs. TIRS-1 • Shape of scattering sources in TIRS-2 is vastly reduced over the shape of the TIRS-1 scattering sources (band 11 shown here) 0.03 Extent of 13-deg scatter source is Recall large greatly reduced from TIRS-1 TIRS-1 13-deg 0.025 scatter source 0.02 A B 0.015 [%] C TIRS-2: 0.03%0.01 (TIRS-1: 0.4%) TIRS-2: 0.01% 0.005 (TIRS-1: 0.024%) 0.00 -20 -10 0 ] 10 20 -10 0 10 20 Angle [Deg] Azimuth [deg 13 TIRS-2 Scattering Magnitude vs. TIRS-1 • Magnitude of the TIRS-2 residual scattering is greatly reduced over the TIRS-1 scatter signal (band 11 shown here) 0.03 -20 TIRS-2: 0.03% -115 (TIRS-1: 0.4%) 0.025 -110 ......., 0.02 C) \ (]) -5 1J L......J A B C 0 0 :+=i 0.015 [%] ct:l > C (]) w 5 TIRS-2: 0.03%0.01 10 (TIRS-1: 0.4%) 15 TIRS-2: 0.01% 0.005 TIRS(TIRS-2:- 1:0.01% 0.024%) 20 (TIRS-1: 0.024%) 0.00 -20 -10 0 10 20 Azimuth [deg] 14 Measured Out-of-field vs. Total • Only able to scan a portion of the out-of-field in TVAC but want to know total scattering signal from all out-of-field sources 0.03 -20 Measured -115 scatter from 0.025 here ......., 0.02 C) (]) 1J L......J A B C 0 :+=i 0.015 [%] ct:l > C (]) w TIRS-2: 0.03%0.01 (TIRS-1: 0.4%) Want to know TIRS-2: 0.01% 0.005 total scatter (TIRS-1: 0.024%) 20 from here 0.00 -20 20 15 Scale Optical Model for Total Signal • Have an optical model of the entire out-of-field scattering source (shown here is the model for detector B, band 11). Measured scatter from here *Can use the measured data to scale the optical model to the appropriate units & sum the model* 16 Total Scattered Signal Estimates • The sum of the scaled optical model for each detector & band yields an estimate of the total scattered signal magnitude: Band 101 Band 11 !Detector-A 0.69 % 1.11 % IDetector-8 0.76 % 1.0,1 % IDetector-C 0.2.4 % 0.21 % • These sums are only an initial estimate of the total scattered signal. • The model is currently being refined for better consistency with TVAC measurements and at a higher spatial resolution. • The estimates for TIRS-2 are well below TIRS-1 values which had sums greater than 8% in some cases. 17 Summary • Baffles added to TIRS-2 optical system to mitigate scattering seen on TIRS-1. • Optical system design changes modeled and tested in laboratory to confirm expected effect at ambient conditions. • Optical design tested under TVAC conditions and confirmed expected result: o Primary scattering source (at 13-deg off-axis) reduced from 0.4% (TIRS-1) to 0.03% (TIRS-2) o Secondary scattering source (at 22-deg off-axis) reduced from 0.024% (TIRS-1) to 0.01% (TIRS-2). • TVAC measurements used to scale magnitude of optical scattering model to estimate approximately 1% total scattered signal in the worst case (further refinements to the model are in progress). 18 References [1] D. Reuter, C. Richardson, F. Pellerano, J. Irons, R. Allen, M. Anderson, M. Jhabvala, A. Lunsford, M. Montanaro, R. Smith, Z. Tesfaye, and K. Thome, “The Thermal Infrared Sensor (TIRS) on Landsat 8: Design Overview and Pre- Launch Characterization,” Remote Sensing, vol. 7, no. 1, pp. 1135–1153, 2015. [2] J.
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