Sandau R. Digital Airborne Camera: Introduction and Technology

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7.1 The ADS40 System 285

Fig. 7.1-5 Cross-section through the Tetrachroid energy beam splitter (2nd generation ADS40 and

3rd generation ADS80)

of CNES. The fact that ATMEL was capable of providing a triple CCD with stag-

gered dual lines was a special challenge. This choice was made consciously with

the intention to use similar algorithms as used in the SPOT 5 satellite to increase the

image resolution by means of staggered lines. It will be possible to fully exploit this

capability once better stabilized platforms become available.

In the case of the ﬁrst generation sensor head it was possible to image the 3 color

channels at the same viewing angle. This made it possible to design different focal

plates of which the two of the four most demanded are pictured in Figs. 7.1-6 and

7.1-7, respectively.

Fig. 7.1-6 The two most demanded types of ﬁrst generation focal plates (location of lines on the

focal plate is not to scale)

7.1 The ADS40 System 287

Fig. 7.1-9 The 2nd

generation sensor head SH51

and/or SH52 of the ADS40

System and 3rd generation

sensor head SH81 and/or

SH82 of the ADS80 System

speciﬁc modules, GNSS receiver, inertial position and attitude processing unit and

mass memory, has been fulﬁlled by the design of the Control Unit CU40 (see

Fig. 7.1-10). This self developed unit fulﬁls many other requirements which are of

large importance to the user.

This includes the following characteristics:

• Low weight,

• Low power consumption

• Small volume

• Few cables

• Robust in handling and reliable in use

• Fulﬁlls the standards of electromagnetic susceptibility in the aircraft

• Remote control of all functions

To fulﬁll the requirement of geo-referenced image strips the Inertial Position

and Attitude System with integrated GNSS receiver and IMU control system was

integrated in the CU40. With this the operator is relieved of the handling of these

two complex systems. By means of a single switch all modules are powered up. A

system test checks every module for availability and functionality. The entire start-

up process is overseen by an environmental controller, which reports to the user if

any module is outside the required operating temperature range or cannot start-up

288 7 Examples of Large-Scale Digital Airborne Cameras

Fig. 7.1-10 The digital

Control Unit CU40

for any other reason. Error warning show the operator if the start-up process was

interrupted.

For decades airborne hyper spectral scanners were equipped with expensive,

unreliable, large and heavy tape recording units. The high cost, weight and volume

of the tape units of the 70’s and 80’s were no longer accepted for airborne use. In

the middle of the 90’s the breakthrough to small, light and power saving hard disks

with more than 150 GB storage capacity reached the market. This eliminated one

of the main obstacles to design a cost-effective airborne digital sensor. Also a 400

Mbit/s data channel including galvanic separation between emitter and receiver was

available by applying glass ﬁber cable technology. Only a thin, light and very robust

glass ﬁber cable connects the CU40 control unit with the sensor head. The connec-

tion of the mass memory MM40 (see Fig. 7.1-11) is established through reliable

and robust multi-pin connector at one end of a slide system on top of the control

unit CU40. Technological progress has made it possible to develop modern mass

memory solutions with the following characteristics:

• Portable mass memories

• Exchangeable during ﬂight

• Memory space for at least 4 h of uninterrupted data acquisition

• Reliable performance up to a ﬂying height of 25,000 ft (7,600 m) without

pressurized cabin.

• Resistant to vibrations and abrupt pressure and temperature changes

Large capacity ﬂash disk technology has evolved into a viable alternative to hard

disks.

7.1 The ADS40 System 289

Fig. 7.1-11 The 0.9 Terabyte

Mass Memory MM40 of the

ADS40

Fig. 7.1-12 Flash Disk MM80 (192 or 384 GB) of the ADS80

The advantages of ﬂash disk technology are:

• reduction of volume and weight (one MM80 weighs 2.5 kg, see Fig. 7.1-12)

• no moving parts

• insensitive to pressure changes

• totally erasable

7.1.2.1 Control Unit CU80 and Mass Memory MM80 for the 3rd generation

ADS80

Compared to earlier generations of the ADS, external and internal interfaces were

reduced to achieve not only simpler integration, but also higher stability. The power

supply to the CU and SH is controlled via a single, central switch. During data

recording in-ﬂight, the incoming data is moved away from the sensor head via

290 7 Examples of Large-Scale Digital Airborne Cameras

the PCIe interface, the Standard Bus System and CPU RAM to the Mass Memory

MM80. This includes image data, information related to the f ocal plate, additional

statistical data from the sensor head, spatial and orientation data from the IPAS20

Position and Attitude System embedded in the CU80, performance data from the

PAV30/80 stabilized mount and ﬂight and system data generated by FCMS, which

supervises and controls the survey ﬂight. In the new Leica ADS80 FCMS is tak-

ing on a much more central role not only in integrating the individual components

such as controlling the power supply to the MM80, ﬂight parameters and sensor

conﬁguration. In addition, FCMS is now taking on the control over the image data,

which are transferred via the Host Bus Adapter to the new MM80 with ﬂash disk

technology. The memory of the CPU RAM is used as a buffer to balance out delays

when writing data onto the MM80. Latest PCIe technology supports the correction

and intelligent management of errors, which contributes signiﬁcantly to guarantee

reliable data recording, management and storage.

The ability of the Leica ADS80 (see Fig. 7.1-13) to achieve ground resolution

better than 5 cm at higher ﬂying speeds requires as higher data throughput as well

as a higher bandwidth for data storage. This is achieved by using several Flash Disks

in one MM80 unit. Currently, the user can choose between MM80 units with 192 or

384 GB data storage capacity. The new CU80 offers space for two adjacent MM80

units, which can be conﬁgured either as joint volumes or as master and backup units.

In addition, a s ingle MM80 can also be used. The MM80 can be exchanged during

ﬂight, thereby offering unlimited data storage. In order to conﬁgure and optimize

data storage performance and data redundancy, a RAID can be generated for data

recording. Data is stored by lines with direct access and not by acquisition time,

which allows the generation of continuous image strips much faster than before.

Compared to earlier hard disk technology the use of ﬂash disks leads not only to

more reliability and performance, but also a weight reduction of some 25 kg at

similar data storage capacity.

7.1.3 Sensor Management

The main characteristics of the user interface of the ADS40/ADS80 Airborne

Digital Sensor are:

• Easy to use

• Central control interface for all functions of the sensor

Because the Inertial Position and Attitude System IPAS, which delivers infor-

mation concerning navigation, drift and location has been totally integrated into

the ADS40/80 the navigation sight used in aerial ﬁlm cameras could be elim-

inated. In its place the Operator Interface (see Fig. 7.1-14) allows the user to

control the system. It allows a comfortable in-ﬂight operation without mouse and

keyboard.

The touch sensitive LCD screen of high luminosity enables the realization of

above mentioned requirements. A special Flight Control and Management Software

7.1 The ADS40 System 291

Fig. 7.1-13 Complete ADS80 System. From left to right: OI80 Operator Interface, CU80 Control

Unit, SH81 Sensor Head, PAV80 Camera Mount

Fig. 7.1-14 The Operator

Interface OI40/OI80

FCMS was developed, which allows the user intuitive access to all functions

with little use of language elements. Clear pictograms guide the users which are

located in many countries around the world. The FCMS software allows a complete

conﬁguration and control of the entire system.

An integrated video camera shows the area which is being over ﬂown and allows

an independent check if the planned ﬂight line is being ﬂown. This visual check also

allows a simple quality control regarding the presence of clouds on the ﬂight line.

292 7 Examples of Large-Scale Digital Airborne Cameras

7.1.4 The Flight Planning and Navigation Software

Fig. 7.1-15 Integrated workﬂow from ﬂight planning to ﬂight execution

The FCMS Flight & Sensor Control and Management System also include Flight

Guidance and the Pilot and Operator Controller OC50 for FCMS, which is used for

all Leica Sensors including Airborne Laser Scanners. The ﬂight plan established

with FPES can be introduced directly into the FCMS of the sensor and the survey

ﬂight will be executed directly from the Operator Interface OI40/80 or the OC50

(Figs. 7.1-15 and 7.1-16).

With the introduction of Leica’s IPAS10 (Inertial Position & Attitude System)

and the Leica FPES (Flight Planning & Evaluation Software) in 2006, the strategy

of offering the user a complete workﬂow of sensor related software was achieved.

The main beneﬁt is a seamless data ﬂow from ﬂight planning to all photogrammetric

applications for all Leica sensors. Training and support cost is thereby reduced when

operating different types of Leica sensors.

Fig. 7.1-16 New FCMS (Flight & Sensor Control Management System) incl. Flight Guidance and

the Pilot and Operator Controller OC50 for FCMS

7.1 The ADS40 System 293

The main tasks of FPES are that ﬂight planning, proposals, ﬂight reporting and

invoicing can be made from the same tool. FPES blends with the FCMS (Flight

& Sensor Control and Management System) and can be used on all types of geo-

graphic and grid coordinate systems. They allow efﬁcient ﬂight planning based on

a DTM for all types of sensors including RC30, ADS40/80, ALS50/60 and other

frame and line sensors as well as sensors operating in an ON/OFF mode. 4 mod-

els of the Leica IPAS10/20 are available for the ADS40/80 and the ALS50/60 and

provide additional functionality like the PPP technology. The introduction of PPP

algorithms/technology into the post-processing of GPS signal observations solves

carrier-phase ambiguities without the need for a base station. This eliminates a logis-

tics restriction associated with GNSS use with airborne sensors and eliminates the

requirement of a DGPS reference station on a known point within 50 km of the

operating sensor. This provides the user greater aircraft disposition ﬂexibility when

capturing imagery of very large and remote areas (forest, desert, plains etc.) and

saves project preparation and operating costs.

7.1.5 The Position and Attitude Measurement System

The Inertial Position and Attitude System IPAS10/20 is completely integrated into

the ADS40/80 system. The IMU is integrated in the sensor heads SH40, SH51/SH52

or SH81/82 where it is rigidly connected to the focal plate (Fig. 7.1-17).

Fig. 7.1-17 View of the SH52/SH82 Sensor Head without housings

294 7 Examples of Large-Scale Digital Airborne Cameras

Table 7.1-1 List of 4 IMU’s (Inertial Measurement Units) from 4 different manufacturers

NUS4 DUS5 NUS5 CUS6

Absolute

accuracy after

post-processing

(RMS)

Position 0.05–0.3 m 0.05–0.3 m 0.05–0.3 m 0.05–0.3 m

Velocity 0.005 m/s 0.005 m/s 0.005 m/s 0.005 m/s

Roll & Pitch 0.008 deg 0.005 deg 0.005 deg 0.0025 deg

Heading 0.015 deg 0.008 deg 0.008 deg 0.005 deg

Relative

accuracy

Angular random

noise

≤0.05 deg/

sqrt(hour)

≤0.01 deg/

sqrt(h)

≤0.01 deg/

sqrt(h)

≤0.01 deg/

sqrt(h)

Drift ≤0.5 deg/h ≤0.1 deg/h <0.1 deg/h <0.01 deg/h

This very rigid table allows the installation of the IMU exactly in the optical axis

of the single telecentric lens of the ADS40/80 which makes the geo-referencing

solution more accurate than in any other large format camera with multiple lenses.

IMU’s from 4 different manufacturers allows the users to adapt to international

exportability restrictions. (Table 7.1-1)

The GNSS/IMU control processor boards are integrated into the Control

Unit CU40/CU80. The operator controls the GNSS/IMU system. All func-

tions of the IPAS10/20 System are controlled automatically by the FCMS

software.

7.1.6 The Gyro Stabilized Mount for the ADS40

The PAV30 mount (Fig. 7.1-18) is worldwide one of the most used for the RC30

Aerial Camera System and is already installed in many aircraft around the world.

For this purpose the PAV30 is equipped with its own inertial stabilization sensors. It

was an obvious choice to use the PAV30 also for the ADS40. This required that the

following additional requirements are also fulﬁlled:

• The total weight of the sensor head of the ADS40 plus and adapter had to be

equal to the RC30

• Vibration damping had to be as good or better than for the RC30

• The PAV30 is required to accept the higher accuracy attitude data from the

Inertial Measurement Unit (IMU), which results in an improved stabilization

performance.

• The Inertial Position and Attitude System IPAS10/20 has to deliver a precise

reference for the automatic drift control of the PAV30.

The lower weight of the sensor heads SH40, SH51 and SH52 is compensated

by means of a mass compensator, which maintains the equal center of gravity and

moment of inertia for the PAV30 as given by the RC30.