skynoise.pro entitlement unlocks the full 10 MHz–350 GHz model range. Licensing changes only the accessible frequency range, not the equations or model fidelity.The selected direction is transformed from local azimuth/elevation to equatorial coordinates and Galactic longitude/latitude for the entered site and time. The private core then calculates exoatmospheric celestial brightness, atmospheric attenuation and emission, and finally integrates the brightness environment through the receiving-antenna power pattern.
| Output | Meaning |
|---|---|
| Exo celestial T | Equivalent Rayleigh–Jeans antenna brightness outside the atmosphere, including diffuse celestial emission and the CMB; Sun/Moon replace the background when the selected ray crosses their disks. |
| Atmospheric contribution | Thermal emission added by the clear gaseous atmosphere along the selected slant path. |
| Clear-sky received T | Atmosphere-attenuated celestial brightness plus gaseous atmospheric emission for the selected pencil-beam direction. |
| Current-weather received T | Clear-sky brightness after the entered rain/cloud attenuation plus the corresponding hydrometeor thermal emission. With rain/cloud set to zero it equals the clear-sky value. |
| Main-beam antenna T | Brightness integrated over the calculated main-beam region. |
| Full-pattern antenna T | 4π pattern-weighted antenna temperature including sky, atmosphere, ground, Sun and Moon. This is the preferred Tant to enter into a link budget when the pattern model is representative. |
The CMB physical thermodynamic temperature is 2.7255 K, but an RF antenna responds to spectral radiance. The tool therefore converts Planck radiance to Rayleigh–Jeans-equivalent noise temperature:
Consequently the CMB equivalent antenna temperature falls below 2.7255 K at millimetre-wave frequencies; this is physical, not a floor or clamp.
The current private core uses a compact 408-MHz directional Galactic morphology and scales the Galactic component approximately as ν^-2.75, consistent with the ITU-R P.372 engineering treatment. The CMB is added with the Planck correction and a small thermal-dust term is included at millimetre wavelengths.
Gaseous absorption is calculated from the ITU-R P.676-13 oxygen and water-vapour spectral-line coefficients. Pressure, temperature and water-vapour density are integrated through a layered ITU-R P.835-7 standard atmosphere, anchored to the entered surface temperature, pressure, relative humidity and site altitude. Curved-Earth geometrical path lengths are used.
Each layer both attenuates the radiation behind it and emits thermally. The core solves the radiative-transfer recurrence from space down to the observer:
Reported gaseous loss and gaseous emission therefore come from the same absorption coefficients and cannot be independently adjusted. The Clear-sky received T row stops at this stage.
The two rain/cloud boxes accept the slant-path attenuation for the selected antenna direction, normally copied from the same ITU-R propagation run used by the satcom link budget: rain from P.618 and cloud from P.840. Scintillation is not entered here because it is an amplitude fading term, not a thermal-emission term.
ITU-R P.618-14 gives the ground-station sky-noise relationship Tsky = Tmr(1−10^(−A/10)) + Tin·10^(−A/10) and the mean radiating temperature estimate:
This app keeps the higher-fidelity P.676 gaseous solution separate, then applies the entered hydrometeor attenuation as an equivalent radiating layer:
Thus the same rain/cloud condition both attenuates the incoming celestial radiation and adds thermal brightness. For the 4π antenna integral, the entered attenuation is exact on boresight; off-boresight sky rays use a plane-parallel slant scaling proportional to sin(El_boresight)/sin(El_ray). A single attenuation value cannot describe the real 3-D structure of a rain cell, so this angular extension is an explicit engineering assumption.
With user override off, the tool uses a quiet-Sun integrated radio-flux spectrum (Benz / Landolt-Börnstein sunspot-minimum data) and log-log interpolates between the two bracketing reference frequencies shown in the readout. There is no hidden F10.7 value. If Use user-supplied solar flux is checked, the entered sfu value at the current operating frequency is used directly.
Solar flux density is converted to disk-averaged equivalent brightness using the finite radio-Sun solid angle:
The Sun is integrated as a finite disk through the antenna pattern. Quiet-Sun predictions do not represent active regions, bursts or flares; EME users with measured/published flux at their operating frequency should use the override.
The Moon is a finite thermal disk. The model uses a frequency-dependent mean disk brightness plus the first harmonic of lunar phase with frequency-dependent thermal phase lag (Krotikov/Pelyushenko-type microwave model). The calculation uses the ephemeris-derived Moon distance and apparent angular diameter. The disk replaces the celestial background behind it, so at low frequencies the Moon can be a negative contrast against a hotter Galactic background.
For an uploaded E/H CSV, the two normalized principal-plane cuts are interpolated into an approximate 3-D power pattern. Two cuts do not uniquely define an arbitrary 3-D pattern, so off-plane sidelobes remain an engineering reconstruction.
For Estimate from gain / SLL, gain and efficiency determine an equivalent aperture/directivity and HPBW; a circular-aperture diffraction pattern is used with sidelobe/backlobe levels constrained by the requested SLL. Gain + SLL cannot uniquely specify a real antenna, so measured/simulated pattern data are preferred for high-accuracy Tant.
The full-pattern integration separately accumulates diffuse sky, atmospheric emission, ground, Sun and Moon contributions. The main-beam figure is the same integration restricted to the modelled main-beam region.
Pattern rays below the local geometric horizon see the entered ground physical temperature and emissivity. A simple Kirchhoff model is used: emitted ground brightness is εT_ground and the reflected fraction (1−ε) uses the mirrored clear-sky brightness. Terrain, buildings, vegetation, radomes and local horizon masks are not modelled.
For an Earth-station receiver, enter the same rain/cloud attenuation condition here that you use for the downlink propagation case, then use Full-pattern antenna T as the satcom app's user-supplied RX antenna temperature when the Sky Noise antenna model represents the real receive antenna. The satcom link budget must still apply gaseous/rain/cloud attenuation to the wanted carrier; Sky Noise uses the attenuation to calculate the associated external receiver noise. These are different physical effects, so this is not double counting.