CN108573120B - Improved simple algorithm for zenith attenuation of electric waves below 350GHz - Google Patents
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- 238000004422 calculation algorithm Methods 0.000 title claims abstract description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 30
- 238000010521 absorption reaction Methods 0.000 claims description 17
- 238000004364 calculation method Methods 0.000 claims description 10
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 9
- 239000001301 oxygen Substances 0.000 claims description 9
- 229910052760 oxygen Inorganic materials 0.000 claims description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 6
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
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Abstract
The invention discloses an improved simple algorithm for zenith attenuation of electric waves below 350GHz, which introduces an equivalent height concept, wherein the equivalent height is an equivalent distance, the atmosphere at the distance is regarded as uniform, the path attenuation of the atmosphere is equal to the zenith attenuation, and the zenith attenuation can be conveniently calculated by utilizing the equivalent height. The improved equivalent altitude model introduces the temperature and humidity of the earth surface to make the earth surface more applicable to different regions. The invention makes the estimation of the attenuation of the ground-air path in millimeter wave and sub-millimeter wave bands more accurate and real-time, because the attenuation on the ground-air path in these frequency bands can not be ignored in the design of the communication link.
Description
Technical Field
The invention relates to a simple and convenient estimation method of zenith attenuation of electric waves below 350GHz, which introduces earth surface temperature and humidity to improve an equivalent height model in ITU-R P.676-11 recommendation and enables the calculation precision of zenith attenuation to be higher and have real-time performance.
Background
In recent years, the development of millimeter wave and sub-millimeter wave band hardware has made it possible to expand the range of applications thereof, such as high-speed satellite-based communication, radar detection, and remote sensing. Therefore, attenuation of the ground-air link must be considered in applications such as communication link design and remote sensing signal analysis.
Since the eighties of the last century, many propagation models have been proposed on the basis of spectral experiments: liebe proposed the MPM (Millimeter-wave amplification Model) Model at the end of the 1980 s; urban proposed a Moliere-5(Microwave occupancy bone Estimation and recovery, version 5) model in 2004; the SARTre ([ Appliximate ] polymeric radiological RadiationTransfer model) model was proposed in J Mendork 2006; the 2008 Japanese institute of communication proposed AMATERASU (model for Atmospherothertz Radiation Analysis and Simulation model); in 2005, p.erikson and s.abuehler proposed arts (adaptive Radiative Transfer simulator) which model was improved until now. However, in the above model, the link calculation of the path attenuation in these frequency bands requires complete path temperature, humidity and pressure or molecular content profile information, which cannot be obtained conveniently. Therefore, a simple approximation model is needed to estimate the path attenuation accurately and conveniently in real time.
For the earth-air path, Suen analyzes the transmission characteristics of THz waves by utilizing atmospheric settleable water vapor, and analyzes the atmospheric attenuation of the global earth-air path. In the ITU-R P.676-11 recommendation, the equivalent altitude is used to make an estimate of the attenuation of the atmospheric path. Where the equivalent height is an equivalent distance over which the path attenuation is equal to the zenith attenuation here. The latter input conditions are more readily available, but the model contains only the atmospheric pressure of the earth's surface, which is not applicable in different climatic and seasonal situations. Since humidity and temperature are the more influential to THz wave propagation. Therefore, in the improved model, the temperature and the humidity are introduced to improve the accuracy of the model and make the model more universal.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method is based on an equivalent height model in the ITU-R P.676 recommendation, and utilizes a model with higher precision and universality, which is improved by the surface temperature, the humidity and the pressure. The present invention is directed to a windowed frequency with greater communication and detection potential.
In order to solve the technical problem, the technical scheme of the invention comprises the following steps:
1) obtaining forward-thrust equivalent heights under the conditions of different profiles by utilizing an atmospheric attenuation model in an ITU-R P.676 recommendation and temperature and humidity pressure profiles in different latitudes and different seasons in the ITU-R P.835;
2) comparing the forward equivalent height with an original equivalent height model to obtain a difference value;
3) fitting the difference curve, and recording a fitting coefficient;
4) correcting the equivalent height coefficient of the dry air by using the temperature to obtain an improved equivalent height model of the dry air;
5) and correcting the water vapor equivalent height coefficient by using the temperature and the humidity to obtain an improved water vapor equivalent height model.
The invention has the beneficial effects that: the improved equivalent altitude model introduces the temperature and the humidity of the earth surface, so that the applicability of the equivalent altitude model to different regions is better, and the estimation of the attenuation of millimeter wave and sub-millimeter wave band ground-air paths is more accurate and has real-time performance.
Drawings
FIG. 1 is a flow chart of a simplified algorithm for improved zenith attenuation of electric waves below 350GHz in accordance with the present invention;
FIG. 2 is a schematic of absorption peak frequencies and window frequencies;
FIG. 3 is a graph of relative error for different atmospheric profiles of equivalent dry air altitude, wherein (a) is standard atmosphere, (b) is low latitude area, (c) is mid-latitude summer, and (d) is high latitude summer;
FIG. 4 is a graph comparing the results of mid-latitude winter dry air calculations, where (a) is the equivalent altitude, (b) is zenith attenuation, and (c) is the relative error;
FIG. 5 is a graph comparing high latitude winter dry air calculations, where (a) is equivalent altitude, (b) is zenith attenuation, and (c) is relative error;
FIG. 6 is a graph of the relative error of different atmospheric profiles for equivalent heights of water vapor, where (a) is standard atmosphere, (b) is low latitude area, (c) is middle latitude summer, and (d) is high latitude summer;
FIG. 7 is a comparison of mid-latitude winter moisture calculations, where (a) is equivalent altitude, (b) is zenith attenuation, and (c) is relative error;
FIG. 8 is a comparison of high latitude winter moisture calculations, where (a) is equivalent altitude, (b) is zenith attenuation, and (c) is relative error.
Detailed Description
Referring to fig. 1, the specific implementation steps for calculating the path attenuation by using the invention are as follows:
as shown in fig. 2, except for the water vapor absorption peaks shown in the figure: 22GHz, 183GHz and 380 GHz; oxygen absorption peak: the frequency bands of 50-70GHz and 118GHz are all frequency windows with smaller absorption. In these frequency bands, the improved equivalent height model has higher precision.
the dry air equivalent height approximation formula based on surface temperature and pressure is written as:
wherein:
t3＝c0+c1f+c2f2+c3f3+c4f4+c5f5(4)
here:
c1＝–0.001968、c2＝5.353×10–5、c3＝–3.707×10–7、c4＝1.03×10–9、c5＝–1.02×10–1，c0the value of (d) is given by:
c0＝-0.14+0.008t (5)
where t is the temperature in degrees Celsius. The limiting and limiting conditions of the model are as follows:
here, the
Wherein p istotRepresenting the total air pressure at the surface of the earth.
calculation of atmospheric absorption in ITU-R P.676-11 (appendix 1 of the recommendation) yields attenuation rates in the atmosphere for radio waves at frequencies up to 1THz, the atmospheric absorption attenuation rate being
κa＝κo+κw＝0.1820fN″″(f) dB/km (7)
Wherein: kappaoThe unit (dB/km) is the absorption decay rate under dry air conditions (nitrogen and non-resonant Debye decay due to atmospheric pressure under oxygen only conditions). Kappaw(in dB/km) is the characteristic attenuation at a certain water vapor density. f (in GHz) is the frequency.
N″(f)＝∑SiFi+N″D(f) (8)
Wherein S isiIs the intensity of the ith line, FiIs the curve shape factor and the sum extends to all lines (for f-frequencies above 118.750343GHz oxygen lines, only oxygen lines above 60GHz recombination rate should be included in the summary); n ″)D(f) Is a dry continuous band of nitrogen absorption and Debye spectra due to atmospheric pressure. Calculation of plus N' using superposition of oxygen absorption lines onlyD(f) The sum of (a) represents the dry air absorption decay rate.
Ao＝hoγo(9)
Aois the dry air zenith attenuation.
the water vapor density equivalent height approximate formula based on the surface temperature, the water vapor density and the pressure is written as follows:
hw＝1.66(B+C(h1+h2+h3)) (10)
here, the
Wherein,
B＝42.01244-7.27769ln(t+273.15)+0.030287ρ (15)
C＝10.35695-0.03411(t+273.15)+0.043366ρ (16)
where ρ is the water vapor density in g/m3。
Step 6, calculating the water vapor attenuation rate by using the annex 1 of the ITU-R P.676-11 recommendation:
and (4) superposing the water vapor spectral lines in the step (3) to obtain the water vapor absorption attenuation rate.
Step 7, multiplying the equivalent height of the water vapor by the attenuation rate to obtain the attenuation of the water vapor zenith;
Aw＝hwγw(17)
Awis the dry air zenith attenuation.
And 8, adding the dry air and the water vapor zenith attenuation to obtain the total atmospheric attenuation at the frequency.
The total atmospheric zenith attenuation is:
A＝Ao+Aw(18)
the effects of the present invention can be further illustrated by the following simulations:
1. simulation conditions and simulation contents:
the improved equivalent altitude model was verified using the warm and humid pressure profiles at different latitudes and in different seasons in ITU-R p.835.
2. Simulation experiment results:
two equivalent height models were validated based on the profile in ITU-R p.835-5, as shown in fig. 3-8. From the curve of the relative error, the accuracy of the new model is improved to different degrees under different atmospheric profiles, and particularly in winter with medium and high latitude, the relative error is reduced from more than 20% to about 10% even approaching 50%. Therefore, the invention is more suitable for different atmospheric conditions, and the input parameters are easy to obtain, so that the zenith attenuation is more real-time.
Claims (2)
1. An improved simple algorithm for zenith attenuation of electric waves below 350GHz comprises the following steps:
1) determining the window frequency with the frequency less than 350GHz and the detector in the zenith direction;
2) calculating the equivalent height of the dry air by using an approximate formula of the equivalent height of the dry air based on the surface temperature and the pressure;
3) calculating the dry air attenuation rate by using a calculation method for atmospheric absorption in annex 1 of the ITU-R P.676-11 recommendation;
4) multiplying the equivalent height of the dry air by the attenuation rate to obtain the attenuation of the zenith of the dry air;
5) calculating the water vapor equivalent height by using a water vapor equivalent height approximation formula based on the surface temperature, the water vapor density and the pressure intensity and the surface atmospheric temperature, the pressure intensity and the water vapor density;
6) calculating the water vapor attenuation rate;
7) multiplying the equivalent height of the water vapor by the attenuation rate to obtain the attenuation of the water vapor zenith;
8) adding the attenuation of the dry air and the water vapor zenith to obtain the total atmospheric attenuation at the frequency;
the dry air equivalent height approximate formula based on the surface temperature and the pressure in the step 2) is as follows:
wherein:
t3＝c0+c1f+c2f2+c3f3+c4f4+c5f5(4)
c1＝–0.001968、c2＝5.353×10–5、c3＝–3.707×10–7、c4＝1.03×10–9、c5＝–1.02×10–1，
c0the value of (d) is given by:
c0＝-0.14+0.008t (5)
wherein t is temperature in units of;
the limiting conditions of the model are as follows:
f<at 70GHz
Where f is the frequency of the wave, in GHz,
wherein p istotRepresents the total gas pressure at the earth's surface;
in the step 3), the absorption attenuation rate of the atmosphere is as follows:
κa＝κo+κw＝0.1820fN″(f) dB/km (7)
wherein: koThe unit dB/km is the absorption attenuation rate under the condition of dry air; kwThe unit dB/km is the characteristic attenuation under the condition of certain water vapor density, and the unit f GHz is the frequency;
N″(f)＝∑SiFi+N″D(f) (8)
wherein S isiIs the intensity of the ith line, FiIs the curve shape factor and the sum extends to all lines, for f-frequencies above 118.750343GHz oxygen lines, only oxygen lines above 60GHz recombination rate should be included in the summary; n ″)D(f) Is a dry continuous band of nitrogen absorption and Debye spectra due to atmospheric pressure; calculation of plus N' using superposition of oxygen absorption lines onlyD(f) The sum of (1) represents the dry air absorption decay rate;
the water vapor equivalent height approximation formula based on the surface temperature, the water vapor density and the pressure in the step 5) is as follows:
hw＝1.66(B+C(h1+h2+h3)) (9)
here, the
Wherein,
B＝42.01244-7.27769ln(t+273.15)+0.030287ρ (14)
C＝10.35695-0.03411(t+273.15)+0.043366ρ (15)
where ρ is the water vapor density in g/m3。
2. The improved simplified algorithm for zenith attenuation of electric waves below 350GHz according to claim 1, wherein the total atmospheric zenith attenuation is:
A＝hoγo+hwγw(16)
wherein, γoAnd gammawRespectively, oxygen and water vapor attenuation rates.
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| US4611929A (en) * | 1983-03-21 | 1986-09-16 | The United States Of America As Represented By The Secretary Of The Navy | Satellite method for measuring sea surface temperature |
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