Radiation level reporting system
This is a continuation of application Ser. No. 667,068 filed Nov. 1, 1984, now abandoned, which is a continuation of application Ser. No. 298,979 filed Sept. 3, 1981, now abandoned. 
    
    
     TECHNICAL FIELD 
     The present invention pertains to the field of remote sensing transponders and in particular to an interregator-responder signaling system for remotely sensing and transmitting preselected parameters. 
     BACKGROUND ART 
     In the event of general nuclear war all strageic airborne elements of the Air Force, including reserve forces, will eventually need a recovery airfield if they are to be retained as assets. One major problem that surviving command and control elements and the force elements themselves have, will be the location of suitable airfields to be used as recovery bases. Starting in the early post-attack period of a general nuclear war, aircraft which are acting under the direction of command and control elements, or, in some cases aircraft that are acting alone will begin collecting information as to the status of all candidate recovery airfields. 
     In the case of the military need for the status of recovery airfields, the information required from the field is the result of nuclear events affecting the airfield, such as, ground radiation level, likelyhood of blast damage, etc. In addition, aircraft attempting to use the field will require a positve means of locating the field in a timely manner where normal ground navigation aids may be inoperative. 
     In the case of civil need, the same nuclear effects information is required. Additional information such as quantity and status of logistic assets may also be required. 
     Because of the nature of the nuclear effects about which information is required and the austere environment of the post-attack period, it is desirable to determine the field status remotely without the need to send survey teams directly to those locations. It is also important to have a system which will provide the status information only to those personnel who are authorized to have it. 
     In view of the above, there exists a need for a simplified system which would provide limited status reporting capability and can interface with an aircraft flying in the vicinity of a potential recovery airfield. This system would provide aircraft personnel with the status of current radiation level and possible surface nuclear effects such as blast overpressure. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus which could be integrated into existing airbourne communications systems for use in determining radiation levels and possible nuclear blast occurances in the vicinity of recovery airfields. A transponder is provided which contains a radiation detector and a pressure sensor. The transponder is positioned on the ground adjacent to the recovery airfield with the radiation detector monitoring radiation levels and initiating generation of a preselected tone relating to the magnitude of the measured radiation level. 
     A conventional airbourne system of an aircraft could be modified to include apparatus of the present invention for interrogating the transponder to determine such monitored surface radiation levels. 
     Upon receipt of an interrogation signal, the transponder&#39;s transmitter will reply with a signal compatible with the airbourne communications system but impressed with the preselected signal indicative of the radiation level magnitude. 
     Additionally, a pressure sensor having a threshold set to be activated on the occurance of nuclear blast overpressures will, upon detection of such overpressure, generate a second different modulating signal indicating that possible nuclear blast damage has occured in the vicinity of the airfield. 
     As some recovery airfields may be in remote and uninhabited areas, the apparatus may be supplied in a parachute-deliverable package which would permit aircraft personnel to perform an air drop to position the equipment adjacent to the airfield, after which the above described radiation measurement and interrogation would occur. 
     Accordingly, it is a feature of the present invention to provide a method and apparatus to determine the presence of radiation adjacent to a recovery airfield. 
     Another feature of the present invention is to provide a method and apparatus for detecting nuclear blast overpressures indicative of damage to the airfield. 
     Yet another feature of the present invention is to provide an automated method and apparatus for measuring radiation and detecting pressure levels which may be incorporated into existing airborne communications equipment such as that found on the type of aircraft utilizing the recovery airfield. 
     These and other features and advantages of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In order that the manner in which the above-recited advantages and features of the invention are attained can be understood in detail, a more particular description of the invention may be had by reference to specific embodiments thereof which are illustrated in the appended drawings which form a part of this specification. It is to be noted however, that the appended drawings illustrate only typical embodiments of the invention and therefore are not to be considered limiting of its scope when the invention may admit to further equally effective embodiments. 
     In the drawings: 
     FIG. 1A is a pictoral representation of the interrogation/response transmission links between an aircraft and a transponder incorporating the present invention. 
     FIG. 1B is a pictoral representation of the parachute air delivery aspect of the present invention. 
     FIG. 2 is a simplified block diagram showing the transponder and interrogator portions of the present invention and indicating the transmission directions of the interrogation/response communications links. 
     FIG. 3 is a simplified block diagram showing the interface between the radiation level detector and the transponder transmitter and indicating the various modulating tones utilized to indicate radiation levels detected by the present invention. 
    
    
     DETAILED DESCRIPTION 
     In the following description, like reference numerals refer to like elements throughtout the various views of the drawings. 
     It is envisioned that the present invention will be incorporated into existing air navigation marker beacon systems. Such marker beacons normally serve to identify a particular location in space along an airway or on the approach of an instrumented runway. This is done by means of a 75 MHz transmitter which continually transmits a directional signal to be received by aircraft flying overhead. These markers are generally used in conjunction with enroute navigation aids and Instrument Landing Systems as point designators. Practice of the invention requires that an aircraft communications radio transmit a preselected interrogation signal, and, upon such transmission, receive via a response an indication of the surface radiation level at preselected airfields while flying overhead within transmission range of a transmitter located proximate to the airfield. Accordingly, the present invention is intended to be used primarily during the post-attack period of a nuclear war, except for brief test periods. Additionally, as in all likelihood the airfield may be damaged by an overpressure shock wave from a nearby nuclear detonation, the marker beacon system should also be modified to detect such over shock waves as an indication of blast damage and transmit that information along with the radiation level information. 
     Referring now to FIGS. 1A and 1B, there is shown an embodiment of the present invention consisting of a crossband transponder 10, and an aircraft 11 equipped with (see FIG. 2) a marker beacon receiver 41 and communications radio 40 forming an airborne communications system 12. A crossband transponder can be generally defined as a transmitter-receiver capable of accepting the challenge of an interrogating signal and automatically transmitting a reply in a different frequency band from that of the received interrogation. In one embodiment of the present invention, the aircraft radio 40 transmits an interrogation signal via RF down link 20, on a preselected frequency, to the transponder 10 which, if it receives and accepts this interrogation signal, will then transmit a 75 MHz signal encoded with radiation level data via RF up link 21 back to the aircraft 11. Aircraft beacon receiver 41 then indicates the radiation level on an ennunciator panel 42 and/or as an aural tone over the crew interphone system 43. 
     The ground transponder 10 is to be located near ground level at designated airfields. Accordingly, transponder 10 may be emplaced permanently at the airfield or, as shown in FIG. B, airdropped using a parachute delivery system 15 to a position adjacent to the airfield of interest. By use of the air delivery method, the aircraft commander is given greater flexibility in his choice of recovery airfields. Additionally, the number of permanent emplacements of the system required to provide sufficient recovery airfields can be greatly reduced. The aircraft 11 must fly within radio range of the transponder 10 for interrogation. The RF link 20 from the aircraft 11 to the transponder 10 should closely match, in sensitivity, the return RF link 21 from the transponder 10 to the aircraft 11 for satisfactory operation. The operational range of the RF link may be any distance from 50 to 200 statute miles and will depend on the power output of the specific transmitting equipment and associated antennas as well as the sensitivity of the receiver equipment and their associated antennas. 
     Referring now to FIG. 2, the transponder 10 consists of a command receiver/controller 31 which decodes and initiates a response to a correct interrogation signal from the aircraft 11. Transponder 10 additionally initiates a power on sequence for turning on other system elements including a radiation measuring device 32 designated to measure gamma radiation. A level detector/ modulator 33 for receiving the output of the radiation measuring set 32 (as will be hereinafter described in greater detail) and generating one of three preselected tones as a modulating signal (FIG. 3). 
     There is included a radio beacon transmitter 34 to accept the tone modulation from modulator driver 58 and radiate a 75 MHz RF signal, modulated by the preselected modulating signal, to the aircraft 11. Transponder 10 further includes a pressure sensor 35 as well as a battery 36 energizing a suitable power supply (not shown) to supply power for the transponder. If transponder 10 is set up in a permanent emplacement a battery charger 37 is supplied and connected to commercial AC power to keep the battery charged to capacity. Alternatively, for a permanent emplacement the battery 36 and charger 37 may be with power supply (not shown) connected directly to a commercial AC power source. 
     When the transponder 10 is configured for air delivery as shown in FIG. lb, the system is also operated by a primary battery 36 energizing the power supply. However, in this case the charger 37 is not required and may not be supplied. The transponder 10 elements are intended to be housed in an air-deliverable environmental enclosure 38. 
     In operation, the interrogation sequence begins with the operator in the aircraft 11. The operator selects the predetermined frequency of the transponder 10 on a communications radio 40. The operator then initiates transmission of the proper interrogation code from radio 40. The interrogation code signal is transmitted between antenna 29 via link 20 to antenna 39 of transponder 10. It should be noted that the interrogation code can be made as simple or complex as required. 
     When the correct interrogation signal is received and decoded at the transponder 10 by the command receiver/controller 31 through omnidirectional antenna 39, the following sequence takes place. Power is supplied to the radiation measuring set 32, level detector/modulator 33, and radio beacon transmitter 34. Upon power application, the radiation measuring set 32 initiates a measurement to determine the current level of gamma radiation in the vicinity of transponder 10 and outputs a analog voltage proportioned to the measured gamma radiation level. Level detector/modulator 33 receives and the analog signal from the radiation measuring set 32 and couples the signal into a level detector section 50 (see FIG. 3). Dependent upon the measured radiation level, the analog signal actuates one of three fixed frequency tone modulation signal generators, 52, 54 and 56, having frequencies of 400 hz, 1300 hz and 3000 hz. respectively with the tone frequency corresponding to measured radiation levels whereby a 400 hz tone indicates the measured level is within first preselected range such as 10 to 40 radiation units, a 1300 hz tone indicates the measured level is in a second preselected range i.e., greater than 40 radiation units and a 3000 hz tone indicates the measured level is within a third preselected range that is less than 10 radiation units. These unit levels are used to determine safe exposure times of the aircraft personnel to the measured radiation with a range of 40 units and up being arbitrarily selected as completely unsafe for average exposure. 
     After a fixed time delay, such as a 30-seconds following receipt of the interrogation signal, the command receiver controller 31 keys the radio beacon transmitter 34. A 75 MHz RF carrier modulated with the activated tone from one of the tone generators 52, 54 and 56, is then transmitted for a preselected limited time period, such as 30 seconds, to the aircraft 11 from omnidirectional bipole antenna 39 over RF link 21. 
     If, however, the pressure sensor 35 has been previously exposed to an overpressure greater than a preset value, the command receiver/controller 31 will cause the transponder 10 to so indicate by either not responding to interrogation or by transmitting some preselected indicating signal. 
     The radiation data encoded signal is then transmitted to aircraft 11, where the marker beacon receiver 41 detects the 75 MHz signal and decodes the tone modulation present on the carrier. This tone is then introduced into the crew interphone system 43. Certain models of marker beacon receivers also have an output signal to an annunciator panel 42. This output signal may be used to illuminate an individual light on the panel corresponding to one of the three possible tones received. When a steady light or tone is present for a preselected time period, such as 30 seconds, this indicates the range that the radiation level proximate to the airfield falls within. For example, if the proper indicator is illuminated and a continuous 3,000 cycle tone is heard then the radiation level can be assumed to be in the range of 0 to 10 units. If a second, different indicator is illuminated and a continuous 400 cycle tone is heard then radiation level is in the range of 10 to 40 units. However if a still different indicator is illuminated and a continuous 1,300 cycle tone is heard the radiation level is 40 units or greater. 
     Although specific embodiments have been described in detail hereinbefore, it is understood that the subject invention is not limited therto and all variations and modifications thereof are contemplated and are included within the scope of the invention as defined by the appended claims.