Aircraft visibility in view from below in the long-wave infrared band using infrared cross section

Mahulikar, Shripad P.; Rastogi, Pallavi; Bhatt, Ashish; Valodi, Shubendu

doi:10.1364/ao.459926

Cited by 5 publications

(8 citation statements)

References 36 publications

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“…Therefore, « sky ¼ 1 and sky-shine irradiance on aircraft SBLE, G sky ¼ e sky (T 1 ) ¼ « sky •e b-sky (T 1 ), IR radiance from SBLE because of reflected G sky : for a complete Earth-disc it can be assumed constant at « ed ¼ 0.93 (Hipps, 1989). For an aircraft bottom surface, Earthshine is more important as it sees the complete Earth-disc (A ed ) because the view factor between the two is high (F bot-ed $ 1) (Mahulikar et al, 2022). However, the wing leading edge, which is a vertical surface of infinitesimal planar-projected area A pl.SBLE sees semi-circular Earth-disc (A ed /2) in front of it.…”

Section: Radiance Because Of External Sourcesmentioning

confidence: 99%

“…Earthshine radiance comprises emission ( e ed ) by virtue of temperature T ed at ε ed and reflection of direct solar radiation (available in daytime) from Earth’s surface. An aircraft at altitude H sees Earth’s surface in the form of a circular disc of area, A ed = π( R vis-ed ) 2 , where the radius of the visible Earth-disc R vis-ed = [ H ·( H + 2 R Earth )] 0.5 /[1+ ( H / R Earth )], and the radius of Earth, R Earth = 6400 km (Mahulikar et al , 2022). Because R vis-ed ≪ R Earth , Earth is assumed to radiate at a constant temperature of T ed = 288.1 K (local ambient temperature at H = 0).…”

Section: Skin Friction Heating Of Wing Leading Edgesmentioning

confidence: 99%

“…sees Earth's surface in the form of a circular disc of area, A ed ¼ p(R vis-ed ) 2 , where the radius of the visible Earth-disc R vis-ed ¼ [H•(H 1 2R Earth )] 0.5 /[11 (H/R Earth )], and the radius of Earth, R Earth ¼ 6400 km(Mahulikar et al, 2022). Because R vis-ed ( R Earth , Earth is assumed to radiate at a constant temperature of T ed ¼ 288.1 K (local ambient temperature at H ¼ 0).…”

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confidence: 99%

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Long wave infrared signature of swept back leading edges in aircraft frontal aspect

Vinayak,

Mahulikar

2024

AEAT

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Purpose In recent years, increased use of all-aspect infrared (IR)-guided missiles based on the long-wave infrared (LWIR; 8–12 µm) band has lowered the probability of aircraft survival in warfare. The lock-on of these highly sensitive missiles is difficult to break, especially from the front. Aerodynamically heated swept-back leading edges (SBLE), because of their high temperature and large area, serve as a prominent LWIR source for aircraft detection from the front. This study aims to report the influence of sweep-back angle (Λ, based on the Mach number [M∞]) on aerodynamic heating and the LWIR signature of SBLE. Design/methodology/approach The temperature along SBLE is obtained numerically as radiation equilibrium temperature (Tw) by discretizing the SBLE length into “n” number of segments, and for each segment, emission based on Tw is evaluated. IR radiance due to reflected external sources (sky-shine and Earthshine) and radiance due to Tw are collectively used to determine the IR contrast between SBLE and its replaced background in the LWIR band (icont-SBLE,LWIR). Findings The results are obtained for low subsonic turboprop aircraft (Λ = 3°, M∞ = 0.44); high subsonic strategic bombers (Λ = 35°, M∞ = 0.8); fifth-generation stealth aircraft (Λ = 40°, M∞ = 1.6); and aircraft with supercruise/supersonic capability (Λ = 50°, M∞ = 2.5). The aircraft with supersonic capability (Λ = 50°, M∞ = 2.5) reports the maximum LWIR signatures and hence the highest visibility from the front. The results obtained are compared with values at Λ = 0° for all cases, which shows that increasing Λ significantly reduces aerodynamic heating and LWIR signatures. Originality/value The novelty of this study comes from its report on the influence of Λ on the LWIR signatures of aircraft SBLE in the frontal aspect for the first time.

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Section: Radiance Because Of External Sourcesmentioning

confidence: 99%

Section: Skin Friction Heating Of Wing Leading Edgesmentioning

confidence: 99%

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confidence: 99%

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Long wave infrared signature of swept back leading edges in aircraft frontal aspect

Vinayak,

Mahulikar

2024

AEAT

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“…31 The τ ed-ac and Π ES for an absorbing atmosphere are estimated analytically based on the procedure proposed by Mahulikar et al. 33 Variation of dimensionless Earthshine, Π ES ðHÞ for a typical atmosphere (using ISA) is in Fig. 5, which shows that Π ES monotonically reduces with increasing H. It reduces rapidly from Π ES ðH ¼ 0Þ ¼ 0.25 to Π ES ðH ¼ 5 kmÞ ¼ 0.0588 and then gradually reduces to Π ES ðH ¼ 14 kmÞ ¼ 0.04235.…”

Section: Estimation Of Earthshine Reflection From Aircraft Nose In Lw-irmentioning

confidence: 99%

“…The τed-ac and ΠES for an absorbing atmosphere are estimated analytically based on the procedure proposed by Mahulikar et al. 33 . Variation of dimensionless Earthshine, ΠES(H) for a typical atmosphere (using ISA) is in Fig.…”

Section: Lwir Signature Of Aircraft Nosementioning

confidence: 99%

Long-wave infrared signature of aircraft nose and its emissivity for low observability

Vinayak

Mahulikar

2023

J. Appl. Rem. Sens.

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High speeds have been an advantage for aircraft to fly out of the adversary's airspace fast, to escape earlier generations of infrared (IR) guided missiles that could lock-on only from the rear aspect. Advancements in IR seekers in long-wave IR (LWIR, 8 to 12 μm) band with imaging sensors in focal plane arrays made them capable of tracking aircraft also from the frontal aspect, which is a tactical advantage. Aerodynamically heated airframe surfaces are LWIR signature hot spots that increase aircraft susceptibility from front and bottom views. The conventional belief is that IR signatures of aircraft nose is only due to temperature-based emission acquired by aerodynamic heating at high Mach number (M amb ). Our study reports the LWIR contrast of aircraft nose (with nose replaced skyshine as background) by considering: (i) aerodynamic heating (important for high ε nose , M amb ) and (ii) reflected skyshine and Earthshine (important at low ε nose , M amb ), where skyshine is more important relative to Earthshine. Earthshine irradiance is obtained using atmospheric transmittance and view factor between visible circular Earth-disc and nose surface. The role of a transition Mach number (M trans ) in emissivity selection is identified as follows: for M amb < M trans , LWIR contrast decreases with ε nose and for M amb > M trans , LW-IR contrast increases with ε nose .

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Multimodal aircraft flight altitude inversion from SDGSAT-1 thermal infrared data

Zhou,

Li,

et al. 2024

Remote Sensing of Environment

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Aircraft visibility in view from below in the long-wave infrared band using infrared cross section

Cited by 5 publications

References 36 publications

Long wave infrared signature of swept back leading edges in aircraft frontal aspect

Long wave infrared signature of swept back leading edges in aircraft frontal aspect

Long-wave infrared signature of aircraft nose and its emissivity for low observability

Multimodal aircraft flight altitude inversion from SDGSAT-1 thermal infrared data

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