The stray light analysis of the sounding of the atmosphere using broadband emission radiometry (SABER) instrument on the thermosphere-ionosphere-mesosphere energetics and dynamics (TIMED) mission is discussed. Relevant mission objectives and operating conditions are stated to define the stray light problem. Since SABER is an earth limb viewing sensor, the telescope must be designed for large off-axis rejection. Described are the key design features which make the instrument well suited for its mission. Representative point source transmittance (PST) curves computed using the commercial stray light program APART are presented. Non-rejected radiance (NRR) values computed using APART generated PST curves and LINEPACK generated curves for the total radiance from the earth aixi the afinosphere are given. A method for computing NRR from the earth and the atmosphere using lineof- sight radiance profiles versus tangent height is described. Computed NRR values demonstrate that the effect of stray light on SABER\u27s measurement capability is negligible

Stauder, John

Esplin, Roy

Zollinger, Lorin

Mlynczak, Marty

Russell, Jim, III

Gordley, Larry

Marshall, Tom

English

Рад се бави истраживањем и анализом ефеката званичне развојне помоћи
државама Подсахарске Африке. Ауторка сарадњу у области развоја између
сиромашних подсахарских држава, и развијених држава које припадају групи
традиционалних међународних донатора, смешта у шири историјски контекст, у
којем она заправо представља само једну од фаза у односима две стране. Ова
последња фаза, фаза тзв. „постмодерног империјализма“, је поред атрибута из
претходног периода, развила и читав низ нових одлика. Позиционирање званиче
развојне помоћи афричким државама у шири историјски контекст, представља
нужан предуслов за разумевање озбиљности развојне кризе са којима се
суочавају постколонијалне афричке државе, као и улоге коју развојна помоћ има
у њеном одржавању, односно продубљивању.
Када је након завршетка Другог светског рата, уследила дезинтеграција
великих европских империја и започео процес деколонизације Африке, отпочело
је и успостављање сложене архитектуре међународне помоћи за развој. Од
успостављања глобалног режима помоћи, па до данас, редистрибуција помоћи за
развој се одвијала унутар граница које су исцртавали, с једне стране себични
интереси богатих држава, и, с друге стране, жеља да се афричка друштва
фундаментално трансформишу према западном моделу, што је, према схватању
донатора, представљало основни предуслов њиховог одрживог економског
развоја.
Развојна помоћ коју обезбеђују међународни донатори, никада није била
безусловна, с тим што је од почетка 1980-их година, условљавање постало
екплицитно, са циљем да се оствари свеобухватно редефинисање
фундаметалних принципа на којима су афричке државе успостављене.
Истовремено, регион Подсахарске Африке је постао регион у којем је интензитет
развојне помоћи, и у историјској али и компаративној перспективи, без
преседена.The dissertation is researching and analysing the effects of official development
assistance (ODA) to Sub-Saharan Africa. Development cooperation between poor
African states, and developed donor countries, gathered in the Development Assistance
Committee, has been positioned within wider historical context, in which it represents
only one of the phases in the relationship between two sides. The latest phase, the
phase of the so called “postmodern imperialism”, along with some attributes inherited
from the previous stages, developed a whole range of new, distinctive features.
Positioning of ODA within the wider context, represents one of the crucial and
therefore necessary preconditions for better understanding of permanent
development crisis of the postcolonial African states, and the role of ODA in its
persistence.
Right after the end of the World War II, the process of the disintegration of the
European empires and decolonization of Africa, was followed by the establishment of
the global aid architecture. Since the establishment of the global aid regime, the
redistribution of ODA has been taking place within the boundaries drawn by the selfish
national interests of the developed countries, but also by the attempt of the
international donor community to fundamentally transform African societies in
accordance with the Western model, which is considered to be a precondition for the
sustainable economic growth and development.
Foreign aid, provided by the developed countries, was never unconditional, but
since the beginning of the 1980s, it has become explicitly conditional in order to
contribute to the fundamental re-conceptualization of the very foundations of the
African societies. At the same time, intensity of the foreign aid to Sub-Saharan Africa is,
historically and comparatively, unprecedented

Vidojević, Jelena S.

National Repository of Dissertations in Serbia (NaRDuS)

Effects of international development assistance to Sub-Saharan Africa

Nardus

DigitalCommons@USU

Utah State University DigitalCommons@USU Space Dynamics Lab Publications Space Dynamics Lab 1-1-1995 Stray Light Analysis of the SABER Telescope John Stauder Roy Esplin Lorin Zollinger Marty Mlynczak Jim Russell III Larry Gordley See next page for additional authors Follow this and additional works at: https://digitalcommons.usu.edu/sdl_pubs Recommended Citation Stauder, John; Esplin, Roy; Zollinger, Lorin; Mlynczak, Marty; Russell, Jim III; Gordley, Larry; and Marshall, Tom, "Stray Light Analysis of the SABER Telescope" (1995). Space Dynamics Lab Publications. Paper 121. https://digitalcommons.usu.edu/sdl_pubs/121 This Article is brought to you for free and open access by the Space Dynamics Lab at DigitalCommons@USU. It has been accepted for inclusion in Space Dynamics Lab Publications by an authorized administrator of DigitalCommons@USU. For more information, please contact digitalcommons@usu.edu. Authors John Stauder, Roy Esplin, Lorin Zollinger, Marty Mlynczak, Jim Russell III, Larry Gordley, and Tom Marshall This article is available at DigitalCommons@USU: https://digitalcommons.usu.edu/sdl_pubs/121 Stray light analysis of the SABER telescopeJohn Stauder, Roy Esplin, Lorin ZollingerSpace Dynamics Laboratory/Uthh State University1695 North Research Park Way, Logan, UT 84341. Marty Mlynczak and Jim Russell ifiNASA Langley Research CenterHampton, VA 23681Larry Gordley and Tom MarshallGATS Inc.28 Research Drive, Hampton, VA 23666ABSTRACTThe stray light analysis of the sounding of the atmosphere using broadband emission radiometry (SABER) instrument on thethermosphere-ionosphere-mesosphere energetics and dynamics (TIMED) mission is discussed. Relevant mission objectives andoperating conditions are stated to define the stray light problem. Since SABER is an earth limb viewing sensor, the telescope mustbe designed for large off-axis rejection. Described are the key design features which make the instrument well suited for its mission.Representative point source transmittance (PST) curves computed using the commercial stray light program APART are presented.Non-rejected radiance (NRR) values computed using APART generated PST curves and LINEPACK generated curves for the totalradiance from the earth aixi the afinosphere are given. A method for computing NRR from the earth and the atmosphere using line-of-sight radiance profiles versus tangent height is described. Computed NRR values demonstrate that the effect of stray light onSABER's measurement capability is negligible.Keywords: APART, LINEPACK, PST, SABER, TIMED, stray light, non-rejected radiance, point source transmittance1. INTRODUCTIONSABER has stringent requirements for the rejection of_______ ________________ ________________ __________off-axis earth and atmospheric radiation which aredriven by the fact that SABER is designed to observelimb emission primarily from the mesosphere and lower_______ ________________ _______________ _________thermosphere, 50 to 150 km in tangent height. Theradiance levels from this region of the atmosphere aregenerally quite small relative to the radiances from thedenser lower atmosphere and from the hard earthsurface. Thus even small amounts of non-rejected, off-_______________ _________axis radiation could seriously compromise the SABERscience measurements.2. INSTRUMENT OVERVIEWThe instrument objectives and parameters of SABERthat are helpful in defming the stray light problem aregiven below. The instrument is described in greater________________ _________depth in a companion paper.'The SABER instrument is a 10-channel earth limbviewing sensor that is to measure atmospheric emissions264 ISPIE Vol. 2553 0819419125/95/$6.OQThe SABER instrument is part of the TIMED mission scheduled for launch in 1998. The sensor is a follow-up to the LIMS instrumentwhich flew on Nimbus 7, however, SABER's sensitivity is expected to be 30 times that of LIMS. This paper discusses the stray lightdesign features and analysis of the SABER instrument.Table 1. SABER Spectral passbands & noise equivalent radiancesChannelNumberChannel Name(Based on atmosphericspecies measured)Spectral Passband(pm)NER(Wcm2sr')1 C02-N 14.888-15.520 1.70E-82 C02-W 13.347-16.941 2.80E-83 C02-W 13.347-16.941 2.80E-84 0 9.057-9.729 l.1OE.85 H20 6.510-7.120 3.70E-96 NO 5.257-5.566 2.50E-97 C02-B 4.197-4.350 1.30E-98 OH-A 1.952-2.189 4.70E-109 OH-B 1.562-1.698 4.70E-1010 02 1.262-1.285 4.70E-10Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/24/2014 Terms of Use: http://spiedl.org/termsStauder, John, Roy Esplin, and Lorin Zollinger. 1995. “Stray Light Analysis of the SABER Telescope.” Proceedings of SPIE 2553: 264–69. doi:10.1117/12.221362. in the 1 to 17 pm spectral range. The telescope, shown in Figure 1, is an on-axis design with a 52% central obscuration. The focallength is 200 mm and the f-number is 2. The earth limb is scanned vertically using a single axis scan mirror. The incoming lightis limited by the aperture stop located at the primary mirror. A chopper that also functions as an intermediate or first field stop islocated at the cassegrain focus. The light is then refocused onto the focal plane by reimaging optics consisting of two mirrors. Thewindow is used to protect the filter and detector assemblies from contamination. The focal plane assembly consists of an array of10 discrete detectors covered by 10 passband filters. The spectral passbands and the required noise equivalent radiance (NER) valuesfor each channel are tabulated in Table 1. Channels 2 and 3 have identical spectral passbands; because of their different locationson the focal plane they have different fields of view and consequently provide a means for correcting spacecraft pointing variations.3. STRAY UGILT DESIGN FEATURESThe reimaging optics of SABER allow for the use of two important design features, an intermediate field stop and a Lyot (glare) stop.The field stop blocks direct radiation, i.e. specular rays, from off-axis sources. Only scattered light from the mirrors, baffles, andmechanical elements located prior to the intermediate stop are allowed to enter the reimaging part of the system. Scattered light fromthese components are reduced as follows: First, the scan, primary, and secondary mirrors are superpolished. Second, a fore baffleSPIE Vol. 2553 / 265BumperLight TrapFore BaffleBumperIFC FullApertureBlackbodyLight TrapSecondary MirrorPrimary MirrorChopper / First FieldAperture StopOutside Surface ofInner Conical BaffleInside Surface ofInner Conical BaffleTertiary MirrorWindowDetector Array —*Figure 1. SABER optical systemDownloaded From: http://proceedings.spiedigitallibrary.org/ on 09/24/2014 Terms of Use: http://spiedl.org/termsis used to minimize the angles that the mirrors can be directly illuminated by off-axis sources. Next, the vane depth and spacing ofthe fore ath mainbaffles are chosen to optimally trap izxident radiation. Finally, the baffle vanes and remaining non-optical elementsare coated with a highly absorptive paint. The other major design feature which suppresses stray light is the use of a cold Lyot stopplaced conjugate with the entrance aperture stop located at the primary mirror. This stop removes diffracted light from the edge ofthe aperture stop and direct scatter from the baffles. The cold Lyot stop also limits the infrared background radiation from withinthe telescope.4. INSTRUMENT STRAYLIGhT PERFORMANCEStray light is the unwanted radiation that reaches a sensor's detector. Unwanted radiation is defined as any radiation that is outsidethe desired field ofview ofthe sensor. The two main sources of stray light for SABER are the thermally emitted radiation from theearth' s surface and emissions from the atmosphere. Other sources include reflected sunlight, or albedo, and thermally emittedradiation from within the telescope. Several paths exist where radiation from these off-axis sources can reach the detector. Theyinclude scattered radiation from optical and non-optical surfaces, diffraction from sharp edges such as the entrance port edge, anddirect illumination as can be the case with internal thermal emissions.Thermal emissions from SABER components located in front of the chopper are neutralized by subtracting the instrument responseto deep space (the instrument zero-signal response) from each earth-limb measurement. Thermal emissions from components afterthe chopper add nothing to the signal because they are unchopped. Thus, to first-other accuracy, thennal emissions from SABERitself are not confused with signal, however they do contribute to the photon noise. So far this photon noise contribution has beenbOunded using first-order techniques, and it is included in the NER values tabulated in Table 1. An APART analysis to refine thisestimate is planned for next year. Thermal emissions from within SABER are not considered further in this paper.The stray light analysis was performed using the APART program from Breault Research Organization, Inc. The dominate straylight paths to the detector are scatter from the scan, primary, aiil secondary mirrors. Minor stray light paths include diffraction fromthe intermediate field stop and Lyot stop edges, and scattered radiation off of the tertiary and quaternary mirrors. A useful outputof APART is the sensor's off-axis response to a point source which is discussed below.The off-axis response of SABER is described by the point source transmission (PSI) curve. The PST curve shown in Figure 2 (solidline) is for channel 3 with a field-of-view tangent height of 100 km. The PST is defined as the power on the detector, as afunctionof a point source's off-axis angle, normalized by the detector power from the point source on-axis, orPd(O)PST(O)= (1)SABER's PST can be interpreted as follows:At off-axis angles less than 5° , scatteredlight off of the rimary and secondarymirrors that is imaged onto the detectordominates. Scattered radiation from the scanmirror reaching the detector becomessignificant at 5° and dominates by 15° . Theresponse steadily decreases with increasingoff-axis angles until the scan mirror becomestotally shielded from the point source by thefore baffle. This is indicated by the rapiddrop in the response after 22° . Multiplescattering paths involving the scan mirroraccount for the remaining off-axis response.These paths include diffraction from theentrance port edge and scatter from the forebaffle knife edges which in turn scatter offthe scan mirror onto the detector. The266 / SP1E Vol. 25531.OOE-04 -4--—— —1.OOE.060—k—1.OOE8-1.OOE-1O ——1.OOE-121.OOE-14——b...———-..1.OOE-161 V1P.12——-—0 10 20 30 40 50 60 70 80 90Off-AxisAngle (degjFigure 2. SABER PST curves with %nd without Lyot stop- -, . wlo LyotStop—u—With Lyot StopDownloaded From: http://proceedings.spiedigitallibrary.org/ on 09/24/2014 Terms of Use: http://spiedl.org/termssteady decline in the response after 22° results from the decrease in illumination of the entrance port edge and fore baffle.To illustrate the importance of the Lyot stop, this design feature was removed from the analysis. The resulting PST curve is alsoshown in Figure 2 (dashed line). Except for the region from 16° to 22° , the off-axis response is more than an order of magnitudebetter when the Lyot stop is utilized. In fact, at angles less than 5° the response is three others of magnitude better. The reason forthe improved performance is that the Lyot stop blocks all of the scattered and diffracted radiation from the aperture stop and aperturestop edge, respectively. So what happens in the 16° to 22° region? At 16° the fore baffle shields the aperture stop from the pointsource, thus reducing the benefits of the Lyot stop. Scan mirror scatter dominates in this region. After 22° ,the advantages of theLyot stop are again realized as multiple scattering paths from the aperture stop are blocked.5. NONREJECTED RADIANCEThe non-rejected radiance (NRR) from the earth and the atmosphere was computed as SABER's field of view was scanned acrossthe earth limb by rotating the scan mirror. The earth-sensor geometry is illustrated in Figure 3, where x1y1z1 is the sensor coordinatesystem, and the x2Y22 coordinate system defines the nadir (-z,) and the local horizon (y). NRR values were computed using thefollowing integralNRR = --i;i 2PST(O)L(h(8,4))sin(O)d0d4 (2)where the vaiables ofintegration 0 and are the polar and azimuthalangles of the senor as defined in the bubble in Figure 3, PST is thepoint source transmittance function, L is the is the line-of-sightradiance from the earth and the atmosphere, and Q is the solid angleof the sensor field of view. PST functions were computed for eachscan mirror angle and each channel using APART. As is often done,the above integral assumes PST values are symmetrical about thebaffle axis; that is, they are independent of the azimuthal angle .Radiance values are assumed to be symmetrical about the center ofthe earth so they are completely detennined by the tangent height. Ascan be seen from Figure 3, the tangent height as a function of thevariables of integration can be computed using the followingequations0v= 0 (3)-(s+R)sin (O)cos (4))u(O,4)) = -sin(O)sin(4)sin() + cos (O)cos (t) (4)-sin(O)sin(4)cos() - cos(O)sin()r(O,4) = u(O,4))v (5)w(O,4)) = v - r(O,4)u(O,4)) (6)Figure 3. Geometry of non-rejected radiance integrationh(O,4)) = lw(O,4))I - R (7)SPIE Vol. 2553 / 267Z2SABER coordinatesystem oriented forclearer view ofintegration variables 9and 4.Xs,X2ziDownloaded From: http://proceedings.spiedigitallibrary.org/ on 09/24/2014 Terms of Use: http://spiedl.org/terms:ccz ion I!dS/ 99Z ooUB!p1 pp*J-uoU P1I'-'°N P Jfl2!I UDI '! 4!OH UUL 01'I OZI 001 08 09 01' OZ 0 )THD—.- 9113 1*13 —'c- z El-ID-'-- ZllD—*- z 1113—.-- c•z flIM tLL •j;' 1flj m qiq iti&TB M9!AJi!9!J JO UOiOUflJ V S puojd oiv Gip Aq pozwiou S9flBA 'pjs 1fldUIOO UJ. •19Um3110 o 9T IOJ p3nb Xjuuxoidd SUO!SSItIJ9 ou9qdsom pjoj jo no puu opqj s,qj.io woij uoinquiuoo uoinb in pum tp &nsn pndwoo pj oq o popp ptr jjyjy rnsn pondwoo SVM Z0 p uoinquuoo opoj ui juuiqo siq .ioj uoU!u!s s UOiIOX9 JjOS 9tjI osnoq s9jrjold oouv!p.i o ; uoqndmoo rn posn oit s.i uossiw un-ij juuiqo ON II .IOJ % j;' SI3M uoinquuoo pj opqj mnunxui ui Jo opqp u JOj pj ndwoo o jypj &usn Xq spuuuqo sqi .ioj 9jqiij9u 9q o punoj S13M opqp ST4111?9 01j2 JO UOIflqUVIOO flJ4 9tU SfljA UOSSUJ9 9UJ1-JBp 1U0s91d91 osjv SQflj1A U1JflS9J tj2 'sI9UumTo JoJ iqt' S! 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At ') RUt? 9 S9jVUA UOt1UO3U! 9111 iCq 9WJ9 UOflO9JIj) 912 U JOIO9A 2tiil 92 ! fl 'JO1O9A J!pBU 91(1 S! A ''F' 0 co I ST £ Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/24/2014 Terms of Use: http://spiedl.org/termsis negligible above tangent heights of 60 km for all channels since it is less than 1 NER. Below 60 km the NRR for somechannelsis more than 1 NER, but the percentage of signal due to NRR actually decreases below 60 km as shown in Figure 5. As can beseen from this figure, NRR is less than 0.2% for tangent heights less than 60 km for all channels except the NO channel. The largerNRR percentage values for this channel are not due to stray light problems but rather are due to the weak emissions in this channel.The sensitivity of this channel would have to be improved to benefit from a better stray light design since for this channel NRR isless than 1 NER for all tangent heights. For the other four channels the percentage increase above 60 km is due to decreasing signalsince the stray light input is decreasing with tangent height as shown in Figure 4. These computed NRR values verify the suitabilityof the SABER stray light design because the effects of stray light on SABER's measurement capability are negligible.100____________________________________________________________________10 * . CH11 ,_r -.-CH2—k- CR3-9(-CH40.1_____________________________________________—*-CH6___________________________________________-.--CH1O0.01___________________________________________________________________0.001 I I I0 20 40 60 80 100 120 140Tangent height in kmFigure5. Percent of signal due to stray light6. CONCLUSIONSThe SABER design allows for the effective use of stray light suppression features. These design features include an intermediate fieldstop and a Lyot stop. Point source transmittance curves were computed using APART for 6 of SABER's 10 channels at scan mirrorangles corresponding to field-of-view tangent heights ranging from 20 to 140 km. The dominant stray light contributors to the non-rejected radiance from the earth and almosphere are scatter from the scan, primary and secondary mirrors. A method was describedfor computing non-rejected radiance from both the earth and the atmosphere by extending the defmition of tangent height to includenegative values. For negative tangent heights the line-of-sight intercepts the earth and the radiance depends on earth and atmosphericemissions as well as atmospheric absorption. Radiance profiles were computed using the line-by-line radiance code LINEPAK.Curves of non-rejection radiance computed using this method indicate that stray light will not affect SABER's measurement capability.SPIE Vol. 2553 / 269Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/24/2014 Terms of Use: http://spiedl.org/terms7. REFERENCES1. Esplin, R., et. al., "SABER Instrument Design Update," SPIE Proceedings, Vol. 2553, 19952. "APART Stray Light Analysis Software Package, Version 9.3," Breault Research Organization, 6400 East Grant Road, Suite 350,Tucson, Arizona, 85715.3. Mlynczak, M. G., D. S. Zaras, and M. Lopez-Puertas, "Rapid computation of spectrally integrated non-LTE limb emission,'t J.Geophys. Res., 99, 25761-25772, 1994.4. Gordley, L.L., B. T. Marshall, and D. A. Chu, "LINEPAK: Algorithm for modeling spectral transmittance and radiance," J.Quant. Spectrosc. Radiat. Transfer, 52, 563-580, 1994.270 / SPIE Vol. 2553Downloaded From: http://proceedings.spiedigitallibrary.org/ on 09/24/2014 Terms of Use: http://spiedl.org/terms