阅读说明：本技术 一种适用飞机几何高度的计算方法 (Calculation method suitable for aircraft geometric height ) 是由 陈广永 卫瑞智 周成中 王弟伟 于 2020-04-24 设计创作，主要内容包括：本发明公开了一种适用飞机几何高度的计算方法,利用流体静力学方程计算在当前时刻t时的飞机的几何高度Hge：<Image he="91" wi="700" file="DDA0002464728560000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>其中：P为当前时刻t时的大气压强；T为当前时刻t时的大气温度；g为当前时刻t时的重力加速度；R为当前时刻t时的通用大气常数；Hge<Sub>tl</Sub>为上一时刻的Hge；P<Sub>tl</Sub>为上一时刻的大气压强；R<Sub>tl</Sub>为上一时刻的通用大气常数。本发明由流体静力学方程计算飞机的几何高度,而不依赖于标准大气模型和温度线性下降假设,可以有效提高前视地形告警的准确性。(The invention discloses a method for calculating the geometric altitude of an airplane, which utilizes a hydrostatic equation to calculate the geometric altitude Hge of the airplane at the current time t: wherein: p is the atmospheric pressure at the current moment t; t is the atmospheric temperature at the current moment T; g is the gravity acceleration at the current moment t; r is a general atmospheric constant at the current moment t; hge tl Hge at the previous time; p tl Atmospheric pressure at the previous moment; r tl Is the universal atmospheric constant at the previous moment. The invention calculates the geometric altitude of the airplane by the hydrostatic equation without depending on a standard atmospheric model and a temperature linear decline hypothesis, and can effectively improve the accuracy of the forward-looking terrain warning.)

1. A method for calculating the geometric altitude of an airplane is characterized by comprising the following steps:

step 1, calculating the geometric altitude Hge of the aircraft at the current time t by using a hydrostatic equation:

wherein:

p is the atmospheric pressure at the current moment t;

t is the atmospheric temperature at the current moment T;

g is the gravity acceleration at the current moment t;

r is a general atmospheric constant at the current moment t;

Hge_tlhge at the previous time;

P_tlatmospheric pressure at the previous moment;

R_tlis the universal atmospheric constant at the previous moment.

2. The method of claim 1, further comprising the steps of:

step 2, compensating the geometric altitude Hge of the aircraft calculated by the hydrostatic equation by using the GPS altitude to obtain the geometric altitude GPSHge after the GPS altitude compensation is used at the current time t:

wherein:

GPSHge is the hydrostatic height after GPS height calibration at the current time t;

hgps is the GPS height at the current time t;

tau is the time constant of the filter at the current moment t;

s is Laplace operator.

3. A method for calculating a geometric altitude of an aircraft according to claim 1 or 2, further comprising the steps of:

step 3, when the aircraft is in a take-off and landing state, compensating the geometric altitude Hge of the aircraft calculated by the hydrostatic equation by using the radio altitude to obtain the geometric altitude RADHge after the radio altitude compensation at the current time t:

RADHge＝Hr+Error_t1

Error＝Hr+DBelev-Hge

wherein:

error is an Error correction factor of the current time t;

Error_t1error correction factor for last moment

Hr is the radio altitude at the current time t;

DBelev is the average of the 9-cell elevations below the aircraft at the current time t.

4. The method of claim 3, further comprising the steps of:

step 4, calculating the geometric altitude htp of the aircraft at the current time t by using the air pressure and the air temperature of the aircraft:

wherein: LM is the rate of temperature decrease specified for International Standard atmosphere, P0 is the sea level pressure, G, specified for International Standard atmosphere₀Sea level gravity acceleration specified for international standard atmosphere, R is the air constant of the dry air, and P is the predicted air pressure; SAT is static atmospheric temperature; hp is the gas pressure altitude.

5. The method for calculating the geometrical altitude of the airplane as claimed in claim 4, further comprising the steps of:

and 5, respectively calculating the precision of Hge, GPSHge, RADHge and htp, calculating a window by using the GPS height and the precision of the GPSHge, comparing the Hge, the GPSHge, the RADHge and htp with the window, and carrying out weighted average according to the respective precision if the Hge, the GPSHge, the RADHge and the GPSHge are in the window to obtain the final geometric height.

6. The method for calculating the geometric altitude of the airplane as claimed in claim 5, wherein the accuracy hgefrom of Hge is:

wherein time is initialized system time, Kt is a time error coefficient, dist is an initialized flight distance, Kd is a dist error coefficient, alt is an initialized height change, Ka is an alt error coefficient, and initial is an initialized estimation error.

7. The method for calculating the geometric altitude of the airplane as claimed in claim 5, wherein the precision GPSHgeVFOM of the GPSHge is as follows:

wherein, time2 is the system time after last tracking, Kt2 is the error coefficient of time2, dist2 is the flight distance after last tracking, Kd2 is the error coefficient of dist2, alt2 is the height change after last tracking, Ka2 is the error coefficient of alt2, and GPSVFOMhold is the geometric height GPSHge during last tracking_tThe accuracy of (2).

8. The method for calculating the geometric altitude of an airplane as claimed in claim 5, wherein the accuracy RADHgeVFOM of RADHge is as follows:

wherein time3 is the system time since the last calibration, Kt3 is the error coefficient of time3, dist3 is the flight distance since the last calibration, Kd3 is the error coefficient of dist3, alt3 is the altitude change since the last calibration, Ka3 is the error coefficient of alt3, DataBase is the accuracy of the terrain DataBase from the last calibration: RadAlt is the accuracy of the estimation of radio height.

9. The method for calculating the geometric altitude of the airplane as claimed in claim 5, wherein the accuracy HtpVFOM of htp is as follows:

wherein dist4 is the flying distance after the last tracking, alt4 is the height change after the last tracking, the flying distance dist4 after the last tracking, Itstability is the initialization error, and Basic is the Basic error.

Technical Field

The invention relates to the design technology in the field of avionics, in particular to a calculation method for determining the geometric height of an airplane in airborne terrain perception and warning system software.

Background

The goal of a Terrain Awareness and Warning System (TAWS) is to maximize the prevention of controlled flight ground impacts while operating at a minimum false alarm rate when the aircraft is flying in mountainous areas and in an obstacle-wooded environment. An important function of the equipment is forward-looking terrain warning, and a typical working scene is shown in figure 1. The function is according to information such as the longitude and latitude, atmospheric pressure height and the aerial carrier gesture of the aerial carrier that receive, according to the algorithm model that different aerial carriers such as helicopter, cargo airplane correspond to generate safe envelope and carry global elevation data in the airborne mass storage and carry out the altitude comparison, when certain point on the safe envelope is less than the topography height, the system sends the reputation and reports an emergency and asks the pilot to make and changes out the maneuver in advance, reduces pilot's operating burden, prevents that controllable flight from hitting the ground, ensures flight safety.

Therefore, the comparison between the safety envelope of the terrain sensing and warning system and the elevation data needs to depend on the accurate geometrical height of the airplane. The geometric height, also called altitude, represents the vertical distance of the aircraft from the mean sea level. Currently, the geometric altitude of an aircraft is generally provided by an aircraft aviation data computer in the form of a proportional barometric altitude by measuring the barometric pressure at the current altitude of the aircraft, referred to the standard air (ISA). ISA is the most representative of the average levels in mid-latitudinal regions. ISA assumes that the atmosphere is static and dry, with air pressure being largely dependent on air temperature, gravity and other physical constants. Because military aircraft often operate in low altitude environments while performing missions, the terrain awareness and warning system operates primarily in the troposphere. The atmospheric temperature of the troposphere (less than 11 km) substantially satisfies the following law: the higher the height, the lower the gas pressure and decreases constantly at a certain rate. Sea level temperature is assumed to be 15 degrees celsius and sea level air pressure is assumed to be 1013.25 millibars. However, the real atmosphere may be far from these assumptions, which results in a large difference between the barometric altitude and the real geometric altitude.

Disclosure of Invention

The invention aims to provide a calculation method suitable for the geometric height of an airplane and capable of effectively improving the accuracy of forward-looking terrain warning in order to realize the relative height analysis of a forward-looking terrain warning safety envelope and a height point in a terrain elevation database so as to generate accurate terrain anti-collision warning.

The invention aims to be realized by the following technical scheme:

a method for calculating the geometric altitude of an airplane comprises the following steps:

step 1, calculating the geometric altitude Hge of the aircraft at the current time t by using a hydrostatic equation:

wherein:

p is the atmospheric pressure at the current moment t;

t is the atmospheric temperature at the current moment T;

g is the gravity acceleration at the current moment t;

r is a general atmospheric constant at the current moment t;

Hge_tlhge at the previous time;

P_tlatmospheric pressure at the previous moment;

R_tlis the universal atmospheric constant at the previous moment.

Further, the method also comprises the following steps:

step 2, compensating the geometric altitude Hge of the aircraft calculated by the hydrostatic equation by using the GPS altitude to obtain the geometric altitude GPSHge after the GPS altitude compensation is used at the current time t:

wherein:

GPSHge is the hydrostatic height after GPS height calibration at the current time t;

hgps is the GPS height at the current time t;

tau is the time constant of the filter at the current moment t;

s is Laplace operator.

Further, the method also comprises the following steps:

step 3, when the aircraft is in a take-off and landing state, compensating the geometric altitude Hge of the aircraft calculated by the hydrostatic equation by using the radio altitude to obtain the geometric altitude RADHge after the radio altitude compensation at the current time t:

RADHge＝Hr+Error_t1

Error＝Hr+DBelev-Hge

wherein:

error is an Error correction factor of the current time t;

Error_t1is the error correction factor of the last moment;

hr is the radio altitude at the current time t;

DBelev is the average of the 9-cell elevations below the aircraft at the current time t.

Further, the method also comprises the following steps:

step 4, calculating the geometric altitude htp of the aircraft at the current time t by using the air pressure and the air temperature of the aircraft:

wherein: LM is the rate of temperature decrease specified for International Standard atmosphere, P0 is the sea level pressure, G, specified for International Standard atmosphere₀Sea level gravity acceleration specified for international standard atmosphere, R is the air constant of the dry air, and P is the predicted air pressure; SAT is static atmospheric temperature; hp is the gas pressure altitude.

Further, comprising the steps of:

and 5, respectively calculating the precision of Hge, GPSHge, RADHge and htp, calculating a window by using the GPS height and the precision of the GPSHge, comparing the Hge, the GPSHge, the RADHge and htp with the window, and carrying out weighted average according to the respective precision if the Hge, the GPSHge, the RADHge and the GPSHge are in the window to obtain the final geometric height.

Preferably, the accuracy hgefcom of Hge is:

wherein time is initialized system time, Kt is a time error coefficient, dist is an initialized flight distance, Kd is a dist error coefficient, alt is an initialized height change, Ka is an alt error coefficient, and initial is an initialized estimation error.

Preferably, the precision GPSHgeVFOM of GPSHge is:

wherein, time2 is the system time after last tracking, Kt2 is the error coefficient of time2, dist2 is the flight distance after last tracking, Kd2 is the error coefficient of dist2, alt2 is the height change after last tracking, Ka2 is the error coefficient of alt2, and GPSVFOMhold is the geometric height GPSHge during last tracking_tThe accuracy of (2).

Preferably, the precision RADHge radhgefom is:

wherein time3 is the system time since the last calibration, Kt3 is the error coefficient of time3, dist3 is the flight distance since the last calibration, Kd3 is the error coefficient of dist3, alt3 is the altitude change since the last calibration, Ka3 is the error coefficient of alt3, DataBase is the accuracy of the terrain DataBase from the last calibration: RadAlt is the accuracy of the estimation of radio height.

Preferably, the accuracy htpvdom of htp is:

wherein dist4 is the flying distance after the last tracking, alt4 is the height change after the last tracking, the flying distance dist4 after the last tracking, Itstability is the initialization error, and Basic is the Basic error.

The invention has the beneficial effects that: the invention solves the problem of inaccurate air pressure height obtained by a computer independently depending on atmospheric data for an airborne terrain sensing and alarming system, can effectively improve the accuracy of the geometrical height of an airplane, further determines the relative position of an alarming envelope and a digital elevation terrain, improves the success rate of the airborne terrain sensing and alarming system alarming and reduces the false alarm rate.

Drawings

Fig. 1 is a working scene diagram of a forward-looking terrain warning function of a helicopter terrain awareness and warning system, and at a certain moment in flight, an airborne embedded computer generates a forward-looking terrain warning envelope (102) according to real-time flight parameters such as longitude, latitude, heading, ground speed, pitch angle and roll angle of a carrier (101) and fixed parameters such as maximum climbing rate of the carrier. The terrain and the altitude of the obstacle (103) are stored in an onboard mass memory, and when the terrain 102 and the obstacle 103 intersect, the carrier is judged to have potential ground collision risk, and a voice alarm is given.

FIG. 2 is a block diagram of an algorithm for calculating hydrostatic altitude.

FIG. 3 is a block diagram of an algorithm for compensating hydrostatic altitude by GPS altitude.

FIG. 4 is a block diagram of an algorithm for compensating hydrostatic altitude by radio altitude.

FIG. 5 is a block diagram of an algorithm for compensating barometric altitude from actual temperature.

FIG. 6 is a block diagram of an algorithm for calculating the rationality of various altitude compensations.

FIG. 7 is a block diagram of an algorithm for determining the final geometric altitude of an aircraft.

Detailed Description

In the method for calculating the geometric altitude of the airplane, the hydrostatic altitude is calculated according to the data of the air pressure, the air temperature and the like. Then, according to different altitude measurement sources (or altitudes indirectly calculated by other sensor data) and the vertical uncertainty of the altitudes, hydrostatic altitudes are compensated, and weighted fusion is calculated according to the vertical uncertainty of the different altitude measurement sources, so that the final geometric altitude of the airplane is obtained. The method specifically comprises the following steps:

step 1, calculating the geometric altitude Hge of the aircraft at the current time t by using a hydrostatic equation, namely the hydrostatic altitude, and calculating the precision of the geometric altitude Hge.

Because the standard atmosphere model and the temperature linear descent assumption are adopted, the air pressure altitude calculated by the atmosphere data computer has obvious error compared with the real geometric altitude of the airplane, and the embodiment calculates the geometric altitude of the airplane by the hydrostatic equation instead of depending on the standard atmosphere model and the temperature linear descent assumption.

The hydrostatic altitude calculation method is based on the atmospheric hydrostatic equation, as shown in fig. 2, and the specific calculation formula is as follows:

wherein:

p is the atmospheric pressure at the current moment t;

hge is the geometric height at the current time t;

t is the atmospheric temperature at the current moment T;

g is the gravity acceleration at the current moment t;

r is a general atmospheric constant at the current moment t;

the above equation is solved by adopting trapezoidal integration, and the following can be obtained:

wherein:

tl being the data of the last time instant, i.e. Hge_tlIs the geometrical altitude, P, of the aircraft at the previous moment_tlIs the atmospheric pressure at the previous moment, R_tlIs the universal atmospheric constant at the previous moment.

The hydrostatic altitude needs to be initialized at the beginning. If the aircraft is on a runway, the hydrostatic altitude should be initialized to the elevation of the current runway location. If the aircraft is already in flight when the algorithm begins operation, the hydrostatic altitude should be initialized to the current GPS altitude.

The calculation accuracy of the hydrostatic height is evaluated by calculating the vertical quality factor. The vertical figure of merit calculation for hydrostatic altitude includes the following four factors:

1. initialized system time

2. Initialized flight distance dist

3. Height change alt after initialization

4. Estimated error after initialization

The coefficients of the error factors are set by analyzing flight test data and weather data. Kt 50 ft/hr, Kd 1.5 ft/haili, and Ka 1.0%, the vertical quality factor for hydrostatic height is calculated as follows:

hydrostatic altitude provides greater accuracy in shorter time and shorter distance conditions, such as aircraft takeoff and landing procedures. Due to the error of the air pressure gradient and the accumulated error caused by the integral, the hydrostatic altitude cannot keep the high-precision geometric altitude output for a long time, so the hydrostatic altitude is generally not used independently, but is compensated by combining factors such as the GPS altitude, the radio altitude, the temperature and the like, so as to obtain a stable and precise altitude output, and the algorithms are described one by one later.

And 2, compensating the geometric altitude Hge of the airplane calculated by the hydrostatic equation by using the GPS altitude to obtain the GPS altitude compensated geometric altitude GPSHge at the current time t, and calculating the precision of the geometric altitude GPSHge.

Because GPS altitude readings contain deliberate variations of human factors, GPS altitude is inaccurate in the short term, however, GPS altitude is typically very stable in the long term. The main source of GPS altitude error is the result of the satellite clock being artificially jittered, which appears as a periodically varying bias with a period of around 5 minutes. The GPS height is output by referring to the average sea level and can be directly used for a terrain perception and warning system. The present invention integrates GPS height with other sensors,to achieve the required accuracy. As described in the previous subsection, the error in the geometric height Hge calculated by the hydrostatic equation increases over time, and is therefore compensated for using GPS height. GPS altitude versus geometric altitude Hge through complementary filtering algorithms_tCompensation is carried out, and a specific calculation formula is as follows:

wherein:

GPSHge is the hydrostatic height after GPS height calibration at the current time t;

hgps is the GPS height at the current time t;

hge is the hydrostatic altitude at the current time t;

tau is the time constant of the filter at the current moment t;

s is a Laplace operator;

the time constant Tau of the filter is a function of the vertical uncertainty (VFOM) of the current GPS height. The lower the GPS VFOM, the smaller the time constant Tau. Therefore, the more accurate the GPS height, the faster the GPS height changes with the GPS height for the output after the hydrostatic height compensation; when the accuracy of the GPS height is reduced, the time constant Tau is increased as the GPS VFOM is higher, and the output value of the GPS height after the hydrostatic height is compensated is closer to the hydrostatic height. When the time constant is infinite, the filter stops tracking.

The output of the filter at this time is:

GPSHge＝Hge+K

wherein:

k is the compensation value of the filter when it was last updated.

The calculation accuracy of the GPS altitude compensation hydrostatic altitude is evaluated by calculating the vertical quality factor. The vertical figure of merit calculation for the GPS altitude compensated hydrostatic altitude includes the following four factors:

1. last tracked system time 2;

2. distance of flight dist2 after the last tracking;

3. the last tracked height change alt 2;

4. and the GPS vertical quality factor GPS VFOM (the GPSVFOMhold) in the last tracking.

The coefficients of the error factors are set by analyzing flight test data and weather data. The vertical quality factor for GPS altitude compensated hydrostatic altitude is calculated for Kt2 ═ 50 ft/hr, Kd2 ═ 1.5 ft/haili, and Ka2 ═ 10 ft/altitude for each 1000 ft change, as follows:

and 3, compensating the geometric altitude Hge of the airplane calculated by the hydrostatic equation by using the radio altitude to obtain the radio altitude compensated geometric altitude RADHge at the current time t, and calculating the precision of the geometric altitude RADHge.

When the airplane is in a take-off and landing state, the geometric altitude Hge of the airplane calculated by the hydrostatic equation can be compensated by using the radio altitude, so that the compensated geometric altitude RADHge is obtained. In flat terrain, the radio altitude can produce the most accurate calibration values. The calibration value RADHge is based on the current radio altitude value and the average terrain elevation value below the aircraft. The specific calculation formula is shown in the following figure:

Error＝Hr+DBelev-Hge

wherein:

error is an Error correction factor of the current time t;

hr is the radio altitude at the current time t;

DBelev is the average value of the elevations of the 9 cells below the airplane at the current time t;

and (3) adding an Error correction factor Error at a moment on the basis of the original hydrostatic height Hge to obtain the corrected hydrostatic height RADHge. Notably, the conditions under which the hydrostatic altitude can be calibrated using the radio altitude are: the aircraft is in an approach mode, the radio altitude is less than 2000 feet, the wings are horizontal, and the distance between the aircraft and the runway is within 10 nautical miles. Unless a more accurate radio altitude value is available, the radio altitude is calibrated only once and remains valid until the aircraft lands.

The calculation accuracy of the radio altitude compensation hydrostatic altitude is evaluated by calculating the vertical quality factor. The vertical figure of merit calculation for radio altitude compensated hydrostatic altitude includes the following four factors:

1. system time since last calibration 3;

2. distance of flight dist3 since the last calibration;

3. height change alt3 since last calibration;

4. the accuracy of the terrain DataBase databank calibrated for the last time, DataBase: an estimate of terrain flatness was obtained by calculating the standard deviation of the 9-cell elevations. On this basis, the superposition of the estimates based on the resolution of the terrain database is considered, with higher resolutions having lower estimates and, if the aircraft is on water, the estimates based on the resolution of the terrain database are set to zero.

5. The estimation precision RadAlt of the radio height Hr at the current time t;

when the calibration is complete, the estimated terrain database accuracy is locked as well as the current aircraft position, altitude, and system time. The calibration value is used until the aircraft passes through the region with the higher accuracy of the estimation database, and the calibration value is reset. The coefficients of the error factors are set by analyzing flight test data and weather data. Kt3, Kd3, 1.5 ft/haii, Ka3, 10 ft/height per 1000 ft of change, the vertical flatness factor for radio altitude compensated hydrostatic altitude is calculated as follows:

and 4, calculating the geometric altitude htp of the airplane at the current time t by using the air pressure and the air temperature of the airplane, and calculating the accuracy of the geometric altitude htp.

One of the main reasons for the inaccuracy of barometric altitude is that atmospheric conditions do not comply with standard atmospheric assumptions. The invention obviously reduces the error of the air pressure altitude by calculating the difference between the actual temperature of the international standard atmosphere and the actual temperature of the environment where the aircraft is located. For standard atmospheric temperature, the calculation formula for the barometric altitude hp is as follows:

wherein:

t0 is the sea level temperature-288.15 k regulated by the international standard atmosphere;

LM is the temperature drop rate specified by the international standard atmosphere-0.0065K/m;

p0 is the atmospheric pressure at sea level-1013.25 mbar specified by the International Standard atmosphere;

g0 is the sea level gravity acceleration specified by international standard atmosphere-9.80665 m/s²；

R is the air constant of the dry air;

p is the predicted pressure.

The accuracy of the above equation depends on the linear temperature drop rate and the standard sea level temperature. The invention improves the accuracy by the actual sea level temperature. The calculation formula for the atmospheric temperature compensated barometric altitude htp is as follows:

wherein:

t0act is the actual sea level temperature.

In practice, it is difficult to obtain the actual sea level temperature. Thus, the actual sea level temperature is estimated from the currently measured temperature, which the method uses to obtain. The calculation formula is as follows:

T_0act＝SAT+hp*LM

wherein:

SAT is static atmospheric temperature

hp is the air pressure altitude

Substituting the above formula into the above formula can obtain:

comparing hp to htp, we can obtain:

namely, it is

htp＝k*hp

It should be noted that the above derivation only corrects for the effect of temperature on barometric pressure altitude.

The calculation accuracy of the temperature compensated barometric height is evaluated by calculating the vertical quality factor. The vertical quality factor calculation of the temperature compensated barometric altitude includes the following four factors:

1. distance of flight dist4 after the last tracking;

2. the last tracked height change alt 4;

3. initializing an error Itstability;

4. basic error Basic.

The vertical quality factor of the temperature compensated barometric altitude is calculated as follows:

it is worth noting that since the pilot corrects the altitude to the local air pressure with which it is placed on the airport runway, the error in the estimation of the corrected altitude is based on the distance and altitude above the runway. Furthermore, the error is not linear: the error rate is greater when approaching the ground, since the interaction of the atmosphere with the ground is more complex than at high altitudes. The coefficient of altitude variation is therefore related to the distance from the airport runway and varies with altitude.

And 5, calculating the final height.

To ensure that unreasonable values are not used in the final calculation of the geometric height values, it is therefore necessary to perform a plausibility check before the final calculation, as shown in fig. 6. Since the GPS altitude provides an estimate of its current accuracy, the invention uses it as a plausibility check for the calculation of other altitudes, specifically using the GPS altitude and its accuracy to calculate a window and comparing the other corrected altitudes to this window to check which data are authentic, altitudes that are not within the range of the GPS altitude will be considered invalid and will not be used in the calculation of the final geometric altitude.

The present invention weights each height signal in the calculation of the final height according to the accuracy of the current value of each height signal. The invention gives greater weight to the height values with higher precision, but does not ignore any of them. The use of a weighted average also prevents excessive jumps in the final height. The weighted average calculation formula for the final geometric altitude of the aircraft is as follows:

wherein:

GPSHge is hydrostatic height after GPS height compensation;

htp is the air pressure height after temperature compensation;

RADHge is the hydrostatic height after radio height compensation;

in this way, the final geometric altitude TAAlt of the aircraft is obtained. In order to express the confidence coefficient of the geometric altitude and embody the error range of the geometric altitude, the vertical uncertainty of the final geometric altitude of the airplane is calculated by utilizing the vertical quality factors of the compensated altitudes, and the calculation is carried out according to the following formula:

through the steps, the accurate geometric altitude of the airplane can be calculated according to parameters such as atmospheric temperature, atmospheric pressure, radio altitude, GPS altitude and the like, compared with the air pressure altitude calculated by a traditional atmospheric data computer, the problem that the air pressure altitude obtained by independently depending on the atmospheric data computer is inaccurate is solved, the accuracy of the geometric altitude of the airplane can be effectively improved, the relative position of an alarm envelope and a digital elevation terrain is further determined, the success rate of airborne terrain sensing and alarm of an alarm system is improved, and the false alarm rate is reduced.